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| author | Dave Hansen <dave.hansen@linux.intel.com> | 2014-12-12 16:58:19 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-12-13 12:42:52 -0800 |
| commit | d3c97900b427b8d5a476fdfe484267f09df418d6 (patch) | |
| tree | 0169510392ae190dcec4376a7341efe955fa27fd | |
| parent | 0050ee059f7fc86b1df2527aaa14ed5dc72f9973 (diff) | |
| download | linux-d3c97900b427b8d5a476fdfe484267f09df418d6.tar.gz linux-d3c97900b427b8d5a476fdfe484267f09df418d6.tar.bz2 linux-d3c97900b427b8d5a476fdfe484267f09df418d6.zip | |
ipc/shm.c: fix overly aggressive shmdt() when calls span multiple segments
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@linux.intel.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | ipc/shm.c | 18 |
1 files changed, 13 insertions, 5 deletions
diff --git a/ipc/shm.c b/ipc/shm.c index 01454796ba3c..e5dc7d246f05 100644 --- a/ipc/shm.c +++ b/ipc/shm.c @@ -1229,6 +1229,7 @@ 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 @@ -1245,7 +1246,8 @@ 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, @@ -1271,8 +1273,14 @@ 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 @@ -1298,8 +1306,8 @@ 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; } |