Commit d3c97900 authored by Dave Hansen's avatar Dave Hansen Committed by Linus Torvalds

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: default avatarDave Hansen <dave.hansen@linux.intel.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Reviewed-by: default avatarDavidlohr Bueso <dave@stgolabs.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0050ee05
...@@ -1229,6 +1229,7 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr) ...@@ -1229,6 +1229,7 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
int retval = -EINVAL; int retval = -EINVAL;
#ifdef CONFIG_MMU #ifdef CONFIG_MMU
loff_t size = 0; loff_t size = 0;
struct file *file;
struct vm_area_struct *next; struct vm_area_struct *next;
#endif #endif
...@@ -1245,7 +1246,8 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr) ...@@ -1245,7 +1246,8 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
* started at address shmaddr. It records it's size and then unmaps * started at address shmaddr. It records it's size and then unmaps
* it. * it.
* - Then it unmaps all shm vmas that started at shmaddr and that * - 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 * Errors from do_munmap are ignored: the function only fails if
* it's called with invalid parameters or if it's called to unmap * 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, * a part of a vma. Both calls in this function are for full vmas,
...@@ -1271,8 +1273,14 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr) ...@@ -1271,8 +1273,14 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
if ((vma->vm_ops == &shm_vm_ops) && 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) {
/*
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); do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start);
/* /*
* We discovered the size of the shm segment, so * We discovered the size of the shm segment, so
...@@ -1298,8 +1306,8 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr) ...@@ -1298,8 +1306,8 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
/* finding a matching vma now does not alter retval */ /* finding a matching vma now does not alter retval */
if ((vma->vm_ops == &shm_vm_ops) && 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); do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start);
vma = next; vma = next;
} }
......
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