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errno: -1 is EPERM, and four places were saying it by accident

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Ctrl-C killed the shell. consoleread() breaks off the read in progress when
SIGINT arrives and returned -1 to do it -- and -1 is -EPERM by the time it
reaches a program, so every program that handles SIGINT by carrying on saw a
permanent error instead of an interrupted call:

    zsh: error on TTY read: operation not permitted
    schinitd: restarting os.schos.console-shell

and the next Ctrl-C did it to the replacement. EINTR now, which is what a
signal-interrupted read is required to give. Verified: Ctrl-C an interruptible
command, shell survives, zero restarts.

Same mistake, same file family: link, unlink, rename and renameat returned -1
on every error path. Callers branch on errno -- `if (unlink(p) < 0 && errno !=
ENOENT)` is the standard shape, and against EPERM it always complains -- which
is why zsh reported failures for things that had worked. They return ENOENT,
EEXIST, EXDEV, EISDIR, ENOTEMPTY and EFAULT now. About ninety other `return -1`s
remain in sys_fs.c; these four are done because these four were what a program
tripped over. /dev/mem's unknown minors return ENODEV rather than -1 too.

/dev/urandom was a linear congruential generator seeded with a **constant**, so
every boot produced the same bytes in the same order -- not weak, the same. A
key, a nonce, a temporary filename: shared with every SchOS machine that had
ever run. Seeded at boot from RDRAND where the CPU has it, from the cycle
counter and the wall clock where it does not, and re-stirred per byte. Still an
LCG and still not a CSPRNG; what changed is the part that was dangerous rather
than merely poor.

**Not fixed, and recorded as such:** rename() still will not replace an existing
target, so zsh's history save fails on every exit after the first. An attempt to
unlink the target first was reverted -- the directory is an HTree, dirunlink
followed by dirlink of the same name did not behave, and it panicked in
filewrite with the old file already gone. Losing both files is worse than
refusing, so it refuses until the HTree's slot reuse is understood.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2
This commit is contained in:
Nexoniarz 2026-09-14 22:12:28 +02:00
commit 75ccf9841c
11 changed files with 330 additions and 42 deletions
Download patch file Download diff file Expand all files Collapse all files

19
kernel/core/console.c
View file

@ -10,6 +10,7 @@
#include "irq.h"
#include "param.h"
#include "traps.h"
#include "errno.h"
#include "spinlock.h"
#include "sleeplock.h"
#include "fs.h"
@ -611,11 +612,27 @@ consoleread(struct inode *ip, uint64 off, char *dst, int n)
ilock(ip);
return 0; // end of input
}
// Interrupted, not forbidden.
//
// This returned -1, and -1 is -EPERM. A read broken off by Ctrl-C
// therefore reached userspace as "operation not permitted", which is a
// permanent error -- so every program that handles SIGINT by carrying on
// saw a fatal one instead and exited:
//
// zsh: error on TTY read: operation not permitted
// schinitd: restarting os.schos.console-shell
//
// and then did it again, because the next Ctrl-C did the same thing. A
// shell that cannot survive Ctrl-C is a shell nobody can use.
//
// EINTR is the answer a signal-interrupted read is required to give, and
// the whole convention -- retry, or return to the caller -- is built on
// getting it rather than something else.
if (myproc()->killed || v->in.abort_read) {
v->in.abort_read = 0;
release(&input_lock);
ilock(ip);
return -1;
return -EINTR;
}
sleep(&v->in.r, &input_lock);
}

20
kernel/core/main.c
View file

@ -221,22 +221,22 @@ kmain(uint32 fb_addr)
// sinit: kthread_create needs a usable process table. From here on Ctrl-G
// on the console answers, with no filesystem mounted and nothing in
// userspace started -- which is the whole point of putting it this early.
// After timeinit(), which is what boot_epoch comes from, and before any
// program can ask for a random byte.
random_init();
netuser_init();
dbg_thread_start();
if (boot_verbose) cprintf("verbose boot: dbg thread started\n");
// The one line a working boot prints.
// The greeting is not printed here.
//
// Everything above this is a kinfo(), which means it is in the klog and not
// on the screen -- the whole boot is still there, it is simply not the first
// thing anybody has to read every morning. What is left is the fact that the
// machine came up, and where the rest went if it did not.
// It was, and it landed before userspace had said anything -- so on a quiet
// boot it was followed by the last few lines of `schinit` and whatever the
// jobs had to say, which is the wrong way round for a line whose whole job is
// to be the last thing you read. It belongs at the end of the thing it is
// announcing, and the end of the thing it is announcing is in userspace.
//
// A verbose boot has already said thirty other things and does not need a
// greeting on top of them.
if (!boot_verbose)
cprintf("\nWelcome to SchOS! (F8 at boot for the full log, or dmesg once you are in)\n\n");
// schinitd prints it, once its RunAtLoad jobs are away. See cmd/schinitd.
mpmain();
}

94
kernel/dev/cdev.c
View file

@ -12,7 +12,84 @@ extern int consoleread(struct inode*, uint64, char*, int);
extern int consolewrite(struct inode*, uint64, char*, int);
extern int mouseread(struct inode*, uint64, char*, int);
static uint64 rseed = 0x2A99554433221100ULL;
// --- /dev/random and /dev/urandom -------------------------------------------
//
// This was a linear congruential generator seeded with a constant, which means
// **every boot produced the same bytes in the same order**. Not weak: the same.
// A program asking for a key, a nonce, a temporary filename or a hash seed got
// one it shared with every other SchOS machine that had ever run.
//
// What is here now is still not a CSPRNG and does not pretend to be. It is an
// LCG that is *seeded* from something real and re-stirred from the cycle
// counter on every read, which fixes the one property that made the old one
// dangerous rather than merely poor. See "What it does not do" in
// docs/architecture/devices.md.
static uint64 rseed;
static int rseed_ready;
static void rseed_init(void);
// RDRAND, if this CPU has it. CPUID leaf 1, ECX bit 30.
//
// Checked rather than assumed: the instruction faults with #UD on a CPU that
// does not implement it, and "the random device is a kernel panic" is a worse
// failure than a weak seed.
static int
rdrand64(uint64 *out)
{
uint32 a, b, c, d;
unsigned char ok = 0;
uint64 v = 0;
cpuid_leaf(1, &a, &b, &c, &d);
if (!(c & (1u << 30)))
return 0;
// Ten tries, per Intel's own guidance: the instruction is allowed to fail
// when its entropy pool is momentarily empty, and it says so in CF.
for (int i = 0; i < 10; i++) {
asm volatile("rdrand %0; setc %1" : "=r"(v), "=qm"(ok) :: "cc");
if (ok) { *out = v; return 1; }
}
return 0;
}
// Seeded at boot rather than on the first read.
//
// Lazy would work, but it puts the one line that says where the entropy came
// from in the middle of whatever the machine was doing hours later, and it
// makes the first reader pay for the CPUID. Called from main(); the lazy path
// stays as a belt-and-braces for anything that reads before init runs.
void
random_init(void)
{
if (!rseed_ready)
rseed_init();
}
static void
rseed_init(void)
{
uint64 v;
rseed_ready = 1;
if (rdrand64(&v)) {
rseed = v;
kinfo("random: seeded from RDRAND\n");
return;
}
// No RDRAND. The cycle counter is the only thing here that is different on
// every boot and not written down anywhere -- it is not entropy in any
// serious sense, but it is not a constant either, which was the whole
// problem. Mixed with the wall clock so that two machines starting at the
// same instant do not agree.
rseed = rdtsc();
rseed ^= boot_epoch * 0x9E3779B97F4A7C15ULL;
rseed ^= (uint64)(uintptr_t)&rseed;
if (rseed == 0)
rseed = 0x9E3779B97F4A7C15ULL;
kinfo("random: no RDRAND; seeded from the cycle counter and the clock\n");
}
int
nullwrite(struct inode *ip, uint64 off, char *dst, int n)
@ -36,9 +113,16 @@ zeroread(struct inode *ip, uint64 off, char *dst, int n)
int
randomread(struct inode *ip, uint64 off, char *dst, int n)
{
if(!rseed_ready)
rseed_init();
for(int i = 0; i < n; i++){
// Re-stirred from the cycle counter every byte, so two reads a moment
// apart do not continue one sequence -- and so that a process cannot
// predict the next caller's bytes from its own.
rseed ^= rdtsc();
rseed = rseed * 6364136223846793005ULL + 1442695040888963407ULL;
dst[i] = (rseed >> 32) & 0xFF;
dst[i] = (rseed >> 33) & 0xFF;
}
return n;
}
@ -72,7 +156,9 @@ memread(struct inode *ip, uint64 off, char *dst, int n)
case 7: return zeroread(ip, off, dst, n); // /dev/full reads as zeros
case 8:
case 9: return randomread(ip, off, dst, n);
default: return -1;
// Not "operation not permitted", which is what -1 means once it reaches
// userspace. There is no device on this minor.
default: return -ENODEV;
}
}
@ -88,7 +174,7 @@ memwrite(struct inode *ip, uint64 off, char *dst, int n)
case 5:
case 8:
case 9: return nullwrite(ip, off, dst, n);
default: return -1;
default: return -ENODEV;
}
}

88
kernel/sys/sys_fs.c
View file

@ -686,45 +686,76 @@ addr_t sys_mknod(void)
return 0;
}
// link() and rename() answer with real errno values now, and it is worth saying
// why that needed doing.
//
// Every failure in these used to be `return -1`, and -1 is -EPERM by the time
// it reaches a program. So linking a file that does not exist reported
// "operation not permitted" rather than "no such file" -- not a cosmetic
// difference, because a caller distinguishes the two and acts on it.
//
// zsh is how it surfaced. Its history locking links a lockfile and its history
// save renames a temporary over the real file, and on a machine with no
// history yet both legitimately fail the first time:
//
// zsh: locking failed for /root/.zsh_history: operation not permitted
// zsh: failed to write history file /root/.zsh_history.new: operation not
// permitted
//
// -- neither of which is what happened. About ninety other `return -1`s remain
// in this file. These are corrected because these were the ones found, and
// renameat() is corrected alongside rename() because musl's rename() calls it.
addr_t sys_link(void)
{
char name[DIRSIZ], *new, *old;
struct inode *dp, *ip;
if (argstr(0, &old) < 0 || argstr(1, &new) < 0) return -1;
int err = EPERM;
if (argstr(0, &old) < 0 || argstr(1, &new) < 0) return -EFAULT;
begin_op();
if (!(ip = namei(old))) { end_op(); return -1; }
if (!(ip = namei(old))) { end_op(); return -ENOENT; }
ilock(ip);
if (ip->type == T_DIR) { iunlockput(ip); end_op(); return -1; }
// The one place EPERM is right: POSIX names it for a directory.
if (ip->type == T_DIR) { iunlockput(ip); end_op(); return -EPERM; }
ip->nlink++; iupdate(ip); iunlock(ip);
if (!(dp = nameiparent(new, name))) goto bad_link;
if (!(dp = nameiparent(new, name))) { err = ENOENT; goto bad_link; }
ilock(dp);
if (dp->dev != ip->dev || dirlink(dp, name, ip->inum) < 0) { iunlockput(dp); goto bad_link; }
if (dp->dev != ip->dev) { iunlockput(dp); err = EXDEV; goto bad_link; }
if (dirlink(dp, name, ip->inum) < 0) { iunlockput(dp); err = EEXIST; goto bad_link; }
iunlockput(dp); iput(ip); end_op();
return 0;
bad_link:
ilock(ip); ip->nlink--; iupdate(ip); iunlockput(ip); end_op();
return -1;
return -err;
}
// Same correction as link() and rename() above, and in the same path.
//
// **ENOENT is the one that mattered.** A program that removes a file it is not
// sure exists writes `if (unlink(p) < 0 && errno != ENOENT) complain()`, which
// is the standard shape -- and against -1/EPERM every such test took the
// complaining branch. zsh saving its history is one of them, and it went on
// reporting a failure after the history had in fact been written.
addr_t sys_unlink(void)
{
struct inode *ip, *dp;
char name[DIRSIZ], *path;
uint off;
if (argstr(0, &path) < 0) return -1;
int err = EPERM;
if (argstr(0, &path) < 0) return -EFAULT;
begin_op();
if (!(dp = nameiparent(path, name))) { end_op(); return -1; }
if (!(dp = nameiparent(path, name))) { end_op(); return -ENOENT; }
ilock(dp);
if (namecmp(name, ".") == 0 || namecmp(name, "..") == 0) goto bad_unlink;
if (!(ip = dirlookup(dp, name, &off))) goto bad_unlink;
// "." and ".." are refused by name, which is what POSIX asks for.
if (namecmp(name, ".") == 0 || namecmp(name, "..") == 0) { err = EINVAL; goto bad_unlink; }
if (!(ip = dirlookup(dp, name, &off))) { err = ENOENT; goto bad_unlink; }
ilock(ip);
if (ip->nlink < 1) panic("unlink: nlink < 1");
if (ip->type == T_DIR && dirempty(ip) != 1) { iunlockput(ip); goto bad_unlink; }
if (dirunlink(dp, name, off) < 0) { iunlockput(ip); goto bad_unlink; }
if (ip->type == T_DIR && dirempty(ip) != 1) { iunlockput(ip); err = ENOTEMPTY; goto bad_unlink; }
if (dirunlink(dp, name, off) < 0) { iunlockput(ip); err = EIO; goto bad_unlink; }
if (ip->type == T_DIR) { dp->nlink--; iupdate(dp); }
iunlockput(dp); ip->nlink--; iupdate(ip); iunlockput(ip);
end_op(); return 0;
bad_unlink: iunlockput(dp); end_op(); return -1;
bad_unlink: iunlockput(dp); end_op(); return -err;
}
addr_t sys_exec(void)
@ -797,25 +828,32 @@ addr_t sys_rename(void)
char oldname[DIRSIZ], newname[DIRSIZ];
uint off;
struct dirent de;
if (argstr(0, &oldpath) < 0 || argstr(1, &newpath) < 0) return -1;
int err = EPERM;
if (argstr(0, &oldpath) < 0 || argstr(1, &newpath) < 0) return -EFAULT;
begin_op();
if (!(ip = namei(oldpath))) { end_op(); return -1; }
if (!(ip = namei(oldpath))) { end_op(); return -ENOENT; }
ilock(ip);
if (ip->type == T_DIR) { iunlockput(ip); end_op(); return -1; }
// Renaming a directory needs the ".." fixup and the loop check that are
// not written here. EISDIR names what is missing; EPERM did not.
if (ip->type == T_DIR) { iunlockput(ip); end_op(); return -EISDIR; }
ip->nlink++; iupdate(ip); iunlock(ip);
dp_old = nameiparent(oldpath, oldname);
dp_new = nameiparent(newpath, newname);
if (!dp_old || !dp_new || dp_old->dev != ip->dev || dp_new->dev != ip->dev) {
err = (!dp_old || !dp_new) ? ENOENT : EXDEV;
if (dp_old) iput(dp_old);
if (dp_new) iput(dp_new);
goto bad_rename;
}
ilock(dp_new);
if (dirlink(dp_new, newname, ip->inum) < 0) { iunlockput(dp_new); iput(dp_old); goto bad_rename; }
if (dirlink(dp_new, newname, ip->inum) < 0) {
iunlockput(dp_new); iput(dp_old); err = EEXIST; goto bad_rename;
}
iunlockput(dp_new);
ilock(dp_old);
if (!(ip_src = dirlookup(dp_old, oldname, &off))) {
iunlockput(dp_old); ilock(ip); ip->nlink--; iupdate(ip); iunlockput(ip); end_op(); return -1;
iunlockput(dp_old); ilock(ip); ip->nlink--; iupdate(ip); iunlockput(ip);
end_op(); return -ENOENT;
}
iput(ip_src);
memset(&de, 0, sizeof(de));
@ -824,7 +862,7 @@ addr_t sys_rename(void)
ilock(ip); ip->nlink--; iupdate(ip); iunlockput(ip);
end_op(); return 0;
bad_rename:
ilock(ip); ip->nlink--; iupdate(ip); iunlockput(ip); end_op(); return -1;
ilock(ip); ip->nlink--; iupdate(ip); iunlockput(ip); end_op(); return -err;
}
addr_t sys_symlink(void)
@ -1493,26 +1531,28 @@ addr_t sys_renameat(void)
uint off;
struct dirent de;
begin_op();
if (!(ip = at_namei(olddirfd, oldpath))) { end_op(); return -1; }
if (!(ip = at_namei(olddirfd, oldpath))) { end_op(); return -ENOENT; }
ilock(ip);
if (ip->type == T_DIR) { iunlockput(ip); end_op(); return -1; }
if (ip->type == T_DIR) { iunlockput(ip); end_op(); return -EISDIR; }
ip->nlink++; iupdate(ip); iunlock(ip);
dp_old = at_nameiparent(olddirfd, oldpath, oldname);
dp_new = at_nameiparent(newdirfd, newpath, newname);
if (!dp_old || !dp_new || dp_old->dev != ip->dev || dp_new->dev != ip->dev) {
int e = (!dp_old || !dp_new) ? ENOENT : EXDEV;
if (dp_old) iput(dp_old);
if (dp_new) iput(dp_new);
ilock(ip); ip->nlink--; iupdate(ip); iunlockput(ip); end_op(); return -1;
ilock(ip); ip->nlink--; iupdate(ip); iunlockput(ip); end_op(); return -e;
}
ilock(dp_new);
if (dirlink(dp_new, newname, ip->inum) < 0) {
iunlockput(dp_new); iput(dp_old);
ilock(ip); ip->nlink--; iupdate(ip); iunlockput(ip); end_op(); return -1;
ilock(ip); ip->nlink--; iupdate(ip); iunlockput(ip); end_op(); return -EEXIST;
}
iunlockput(dp_new);
ilock(dp_old);
if (!(ip_src = dirlookup(dp_old, oldname, &off))) {
iunlockput(dp_old); ilock(ip); ip->nlink--; iupdate(ip); iunlockput(ip); end_op(); return -1;
iunlockput(dp_old); ilock(ip); ip->nlink--; iupdate(ip); iunlockput(ip);
end_op(); return -ENOENT;
}
iput(ip_src);
memset(&de, 0, sizeof(de));