From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> This patch has been added to the 3.12 stable tree. If you have any objections, please let us know. =============== commit d3c97900b427b8d5a476fdfe484267f09df418d6 upstream. This is a highly-contrived scenario. But, a single shmdt() call can be induced in to unmapping memory from mulitple shm segments. Example code is here: http://www.sr71.net/~dave/intel/shmfun.c The fix is pretty simple: Record the 'struct file' for the first VMA we encounter and then stick to it. Decline to unmap anything not from the same file and thus the same segment. I found this by inspection and the odds of anyone hitting this in practice are pretty darn small. Lightly tested, but it's a pretty small patch. Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> Reviewed-by: Davidlohr Bueso <dave@xxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Jiri Slaby <jslaby@xxxxxxx> --- ipc/shm.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/ipc/shm.c b/ipc/shm.c index 7a51443a51d6..b039a85e2b8d 100644 --- a/ipc/shm.c +++ b/ipc/shm.c @@ -1227,6 +1227,7 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr) int retval = -EINVAL; #ifdef CONFIG_MMU loff_t size = 0; + struct file *file; struct vm_area_struct *next; #endif @@ -1243,7 +1244,8 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr) * started at address shmaddr. It records it's size and then unmaps * it. * - Then it unmaps all shm vmas that started at shmaddr and that - * are within the initially determined size. + * are within the initially determined size and that are from the + * same shm segment from which we determined the size. * Errors from do_munmap are ignored: the function only fails if * it's called with invalid parameters or if it's called to unmap * a part of a vma. Both calls in this function are for full vmas, @@ -1269,8 +1271,14 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr) if ((vma->vm_ops == &shm_vm_ops) && (vma->vm_start - addr)/PAGE_SIZE == vma->vm_pgoff) { - - size = file_inode(vma->vm_file)->i_size; + /* + * Record the file of the shm segment being + * unmapped. With mremap(), someone could place + * page from another segment but with equal offsets + * in the range we are unmapping. + */ + file = vma->vm_file; + size = file_inode(file)->i_size; do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start); /* * We discovered the size of the shm segment, so @@ -1296,8 +1304,8 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr) /* finding a matching vma now does not alter retval */ if ((vma->vm_ops == &shm_vm_ops) && - (vma->vm_start - addr)/PAGE_SIZE == vma->vm_pgoff) - + ((vma->vm_start - addr)/PAGE_SIZE == vma->vm_pgoff) && + (vma->vm_file == file)) do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start); vma = next; } -- 2.3.3 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html