Subject: + ipc-semc-avoid-overflow-of-semop-undo-semadj-value.patch added to -mm tree To: pmladek@xxxxxxx,davidlohr@xxxxxx,jkosina@xxxxxxx,manfred@xxxxxxxxxxxxxxxx From: akpm@xxxxxxxxxxxxxxxxxxxx Date: Tue, 03 Dec 2013 14:47:11 -0800 The patch titled Subject: ipc/sem.c: avoid overflow of semop undo (semadj) value has been added to the -mm tree. Its filename is ipc-semc-avoid-overflow-of-semop-undo-semadj-value.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/ipc-semc-avoid-overflow-of-semop-undo-semadj-value.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/ipc-semc-avoid-overflow-of-semop-undo-semadj-value.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Petr Mladek <pmladek@xxxxxxx> Subject: ipc/sem.c: avoid overflow of semop undo (semadj) value When trying to understand semop code, I found a small mistake in the check for semadj (undo) value overflow. The new undo value is not stored immediately and next potential checks are done against the old value. The failing scenario is not much practical. One semop call has to do more operations on the same semaphore. Also semval and semadj must have different values, so there has to be some operations without SEM_UNDO flag. For example: struct sembuf depositor_op[1]; struct sembuf collector_op[2]; depositor_op[0].sem_num = 0; depositor_op[0].sem_op = 20000; depositor_op[0].sem_flg = 0; collector_op[0].sem_num = 0; collector_op[0].sem_op = -10000; collector_op[0].sem_flg = SEM_UNDO; collector_op[1].sem_num = 0; collector_op[1].sem_op = -10000; collector_op[1].sem_flg = SEM_UNDO; if (semop(semid, depositor_op, 1) == -1) { perror("Failed to do 1st deposit"); return 1; } if (semop(semid, collector_op, 2) == -1) { perror("Failed to do 1st collect"); return 1; } if (semop(semid, depositor_op, 1) == -1) { perror("Failed to do 2nd deposit"); return 1; } if (semop(semid, collector_op, 2) == -1) { perror("Failed to do 2nd collect"); return 1; } return 0; It passes without error now but the semadj value has overflown in the 2nd collector operation. Signed-off-by: Petr Mladek <pmladek@xxxxxxx> Cc: Davidlohr Bueso <davidlohr@xxxxxx> Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> Cc: Jiri Kosina <jkosina@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- ipc/sem.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-) diff -puN ipc/sem.c~ipc-semc-avoid-overflow-of-semop-undo-semadj-value ipc/sem.c --- a/ipc/sem.c~ipc-semc-avoid-overflow-of-semop-undo-semadj-value +++ a/ipc/sem.c @@ -599,7 +599,7 @@ SYSCALL_DEFINE3(semget, key_t, key, int, static int perform_atomic_semop(struct sem_array *sma, struct sembuf *sops, int nsops, struct sem_undo *un, int pid) { - int result, sem_op; + int result, undo, sem_op; struct sembuf *sop; struct sem * curr; @@ -607,7 +607,7 @@ static int perform_atomic_semop(struct s curr = sma->sem_base + sop->sem_num; sem_op = sop->sem_op; result = curr->semval; - + if (!sem_op && result) goto would_block; @@ -616,25 +616,24 @@ static int perform_atomic_semop(struct s goto would_block; if (result > SEMVMX) goto out_of_range; + if (sop->sem_flg & SEM_UNDO) { - int undo = un->semadj[sop->sem_num] - sem_op; - /* - * Exceeding the undo range is an error. - */ + undo = un->semadj[sop->sem_num] - sem_op; + /* Exceeding the undo range is an error. */ if (undo < (-SEMAEM - 1) || undo > SEMAEM) goto out_of_range; + un->semadj[sop->sem_num] = undo; } + curr->semval = result; } 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--; } - + return 0; out_of_range: @@ -650,7 +649,10 @@ would_block: undo: sop--; while (sop >= sops) { - sma->sem_base[sop->sem_num].semval -= sop->sem_op; + sem_op = sop->sem_op; + sma->sem_base[sop->sem_num].semval -= sem_op; + if (sop->sem_flg & SEM_UNDO) + un->semadj[sop->sem_num] += sem_op; sop--; } _ Patches currently in -mm which might be from pmladek@xxxxxxx are ipc-semc-avoid-overflow-of-semop-undo-semadj-value.patch ipc-semc-avoid-overflow-of-semop-undo-semadj-value-fix.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html