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Subject[PATCH] minor bug in ipc/sem.c
try_atomic_semop() corrupts the process id associated with a semaphore
if a semaphore operation with semval==0 (i.e. wait until the semaphore
value becomes zero) blocks.

I've attached a patch against 2.4.2-ac4, it also applies to 2.4.2

--
Manfred--- 2.4/ipc/sem.c Mon Feb 26 21:10:44 2001
+++ build-2.4/ipc/sem.c Mon Feb 26 21:16:00 2001
@@ -248,27 +248,31 @@
for (sop = sops; sop < sops + nsops; sop++) {
curr = sma->sem_base + sop->sem_num;
sem_op = sop->sem_op;
+ result = curr->semval;

- if (!sem_op && curr->semval)
+ if (!sem_op && result)
goto would_block;

- curr->sempid = (curr->sempid << 16) | pid;
- curr->semval += sem_op;
- if (sop->sem_flg & SEM_UNDO)
- un->semadj[sop->sem_num] -= sem_op;
-
- if (curr->semval < 0)
+ result += sem_op;
+ if (result < 0)
goto would_block;
- if (curr->semval > SEMVMX)
+ if (result > SEMVMX)
goto out_of_range;
+ curr->semval = result;
}

if (do_undo)
{
- sop--;
result = 0;
goto undo;
}
+ sop--;
+ while (sop >= sops) {
+ sma->sem_base[sop->sem_num].sempid = pid;
+ if (sop->sem_flg & SEM_UNDO)
+ un->semadj[sop->sem_num] -= sop->sem_op;
+ sop--;
+ }

sma->sem_otime = CURRENT_TIME;
return 0;
@@ -284,13 +288,9 @@
result = 1;

undo:
+ sop--;
while (sop >= sops) {
- curr = sma->sem_base + sop->sem_num;
- curr->semval -= sop->sem_op;
- curr->sempid >>= 16;
-
- if (sop->sem_flg & SEM_UNDO)
- un->semadj[sop->sem_num] += sop->sem_op;
+ sma->sem_base[sop->sem_num].semval -= sop->sem_op;
sop--;
}

@@ -610,7 +610,7 @@
err = curr->semval;
goto out_unlock;
case GETPID:
- err = curr->sempid & 0xffff;
+ err = curr->sempid;
goto out_unlock;
case GETNCNT:
err = count_semncnt(sma,semnum);
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