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authorHelge Deller <deller@gmx.de>2017-08-23 22:37:00 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2017-08-28 16:09:19 -0700
commit79de3cbe9a974e03a02b71da80da9ee0eb15a2d0 (patch)
treea6ce183a8943e54682493b3217a6f8da43aca0fd
parent702e97621ec7e7a36034ebd7a446af04f59d6dee (diff)
fs/select: Fix memory corruption in compat_get_fd_set()
Commit 464d62421cb8 ("select: switch compat_{get,put}_fd_set() to compat_{get,put}_bitmap()") changed the calculation on how many bytes need to be zeroed when userspace handed over a NULL pointer for a fdset array in the select syscall. The calculation was changed in compat_get_fd_set() wrongly from memset(fdset, 0, ((nr + 1) & ~1)*sizeof(compat_ulong_t)); to memset(fdset, 0, ALIGN(nr, BITS_PER_LONG)); The ALIGN(nr, BITS_PER_LONG) calculates the number of _bits_ which need to be zeroed in the target fdset array (rounded up to the next full bits for an unsigned long). But the memset() call expects the number of _bytes_ to be zeroed. This leads to clearing more memory than wanted (on the stack area or even at kmalloc()ed memory areas) and to random kernel crashes as we have seen them on the parisc platform. The correct change should have been memset(fdset, 0, (ALIGN(nr, BITS_PER_LONG) / BITS_PER_LONG) * BYTES_PER_LONG); which is the same as can be archieved with a call to zero_fd_set(nr, fdset). Fixes: 464d62421cb8 ("select: switch compat_{get,put}_fd_set() to compat_{get,put}_bitmap()" Acked-by:: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Helge Deller <deller@gmx.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/select.c6
1 files changed, 1 insertions, 5 deletions
diff --git a/fs/select.c b/fs/select.c
index 9d5f15ed87fe..c6362e38ae92 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -1164,11 +1164,7 @@ int compat_get_fd_set(unsigned long nr, compat_ulong_t __user *ufdset,
if (ufdset) {
return compat_get_bitmap(fdset, ufdset, nr);
} else {
- /* Tricky, must clear full unsigned long in the
- * kernel fdset at the end, ALIGN makes sure that
- * actually happens.
- */
- memset(fdset, 0, ALIGN(nr, BITS_PER_LONG));
+ zero_fd_set(nr, fdset);
return 0;
}
}