From 247a8ce8229b16d4ffa9f5125fb6583aa749679d Mon Sep 17 00:00:00 2001 From: Manfred Spraul Date: Fri, 6 Jun 2014 14:37:38 -0700 Subject: [PATCH] ipc/shm.c: check for ulong overflows in shmat The increase of SHMMAX/SHMALL is a 4 patch series. The change itself is trivial, the only problem are interger overflows. The overflows are not new, but if we make huge values the default, then the code should be free from overflows. SHMMAX: - shmmem_file_setup places a hard limit on the segment size: MAX_LFS_FILESIZE. On 32-bit, the limit is > 1 TB, i.e. 4 GB-1 byte segments are possible. Rounded up to full pages the actual allocated size is 0. --> must be fixed, patch 3 - shmat: - find_vma_intersection does not handle overflows properly. --> must be fixed, patch 1 - the rest is fine, do_mmap_pgoff limits mappings to TASK_SIZE and checks for overflows (i.e.: map 2 GB, starting from addr=2.5GB fails). SHMALL: - after creating 8192 segments size (1L<<63)-1, shm_tot overflows and returns 0. --> must be fixed, patch 2. Userspace: - Obviously, there could be overflows in userspace. There is nothing we can do, only use values smaller than ULONG_MAX. I ended with "ULONG_MAX - 1L<<24": - TASK_SIZE cannot be used because it is the size of the current task. Could be 4G if it's a 32-bit task on a 64-bit kernel. - The maximum size is not standardized across archs: I found TASK_MAX_SIZE, TASK_SIZE_MAX and TASK_SIZE_64. - Just in case some arch revives a 4G/4G split, nearly ULONG_MAX is a valid segment size. - Using "0" as a magic value for infinity is even worse, because right now 0 means 0, i.e. fail all allocations. This patch (of 4): find_vma_intersection() does not work as intended if addr+size overflows. The patch adds a manual check before the call to find_vma_intersection. Signed-off-by: Manfred Spraul Acked-by: Davidlohr Bueso Acked-by: KOSAKI Motohiro Acked-by: Michael Kerrisk Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/shm.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/ipc/shm.c b/ipc/shm.c index 2b64b0d25bba..dda8f1ff3c35 100644 --- a/ipc/shm.c +++ b/ipc/shm.c @@ -1160,6 +1160,9 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr, down_write(¤t->mm->mmap_sem); if (addr && !(shmflg & SHM_REMAP)) { err = -EINVAL; + if (addr + size < addr) + goto invalid; + if (find_vma_intersection(current->mm, addr, addr + size)) goto invalid; /* -- 2.30.2