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author | Al Viro <viro@ZenIV.linux.org.uk> | 2016-09-20 20:07:42 +0100 |
---|---|---|
committer | Sasha Levin <alexander.levin@verizon.com> | 2016-10-03 12:58:36 -0400 |
commit | 01e893ae13ae22a799e3323445af759bbf00381d (patch) | |
tree | 64de0fb7c212d98891d19a1f42407b4630f4be46 | |
parent | 8b915554cd8533de3ad32b2294d62be257a9c2bf (diff) | |
download | lwn-01e893ae13ae22a799e3323445af759bbf00381d.tar.gz lwn-01e893ae13ae22a799e3323445af759bbf00381d.zip |
fix fault_in_multipages_...() on architectures with no-op access_ok()
[ Upstream commit e23d4159b109167126e5bcd7f3775c95de7fee47 ]
Switching iov_iter fault-in to multipages variants has exposed an old
bug in underlying fault_in_multipages_...(); they break if the range
passed to them wraps around. Normally access_ok() done by callers will
prevent such (and it's a guaranteed EFAULT - ERR_PTR() values fall into
such a range and they should not point to any valid objects).
However, on architectures where userland and kernel live in different
MMU contexts (e.g. s390) access_ok() is a no-op and on those a range
with a wraparound can reach fault_in_multipages_...().
Since any wraparound means EFAULT there, the fix is trivial - turn
those
while (uaddr <= end)
...
into
if (unlikely(uaddr > end))
return -EFAULT;
do
...
while (uaddr <= end);
Reported-by: Jan Stancek <jstancek@redhat.com>
Tested-by: Jan Stancek <jstancek@redhat.com>
Cc: stable@vger.kernel.org # v3.5+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
-rw-r--r-- | include/linux/pagemap.h | 38 |
1 files changed, 19 insertions, 19 deletions
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 4b3736f7065c..30a8f531236c 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -594,56 +594,56 @@ static inline int fault_in_pages_readable(const char __user *uaddr, int size) */ static inline int fault_in_multipages_writeable(char __user *uaddr, int size) { - int ret = 0; char __user *end = uaddr + size - 1; if (unlikely(size == 0)) - return ret; + return 0; + if (unlikely(uaddr > end)) + return -EFAULT; /* * Writing zeroes into userspace here is OK, because we know that if * the zero gets there, we'll be overwriting it. */ - while (uaddr <= end) { - ret = __put_user(0, uaddr); - if (ret != 0) - return ret; + do { + if (unlikely(__put_user(0, uaddr) != 0)) + return -EFAULT; uaddr += PAGE_SIZE; - } + } while (uaddr <= end); /* Check whether the range spilled into the next page. */ if (((unsigned long)uaddr & PAGE_MASK) == ((unsigned long)end & PAGE_MASK)) - ret = __put_user(0, end); + return __put_user(0, end); - return ret; + return 0; } static inline int fault_in_multipages_readable(const char __user *uaddr, int size) { volatile char c; - int ret = 0; const char __user *end = uaddr + size - 1; if (unlikely(size == 0)) - return ret; + return 0; - while (uaddr <= end) { - ret = __get_user(c, uaddr); - if (ret != 0) - return ret; + if (unlikely(uaddr > end)) + return -EFAULT; + + do { + if (unlikely(__get_user(c, uaddr) != 0)) + return -EFAULT; uaddr += PAGE_SIZE; - } + } while (uaddr <= end); /* Check whether the range spilled into the next page. */ if (((unsigned long)uaddr & PAGE_MASK) == ((unsigned long)end & PAGE_MASK)) { - ret = __get_user(c, end); - (void)c; + return __get_user(c, end); } - return ret; + return 0; } int add_to_page_cache_locked(struct page *page, struct address_space *mapping, |