3.16.57-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Joe Lawrence joe.lawrence@redhat.com
commit d3f14c485867cfb2e0c48aa88c41d0ef4bf5209c upstream.
round_pipe_size() contains a right-bit-shift expression which may overflow, which would cause undefined results in a subsequent roundup_pow_of_two() call.
static inline unsigned int round_pipe_size(unsigned int size) { unsigned long nr_pages;
nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT; return roundup_pow_of_two(nr_pages) << PAGE_SHIFT; }
PAGE_SIZE is defined as (1UL << PAGE_SHIFT), so: - 4 bytes wide on 32-bit (0 to 0xffffffff) - 8 bytes wide on 64-bit (0 to 0xffffffffffffffff)
That means that 32-bit round_pipe_size(), nr_pages may overflow to 0:
size=0x00000000 nr_pages=0x0 size=0x00000001 nr_pages=0x1 size=0xfffff000 nr_pages=0xfffff size=0xfffff001 nr_pages=0x0 << ! size=0xffffffff nr_pages=0x0 << !
This is bad because roundup_pow_of_two(n) is undefined when n == 0!
64-bit is not a problem as the unsigned int size is 4 bytes wide (similar to 32-bit) and the larger, 8 byte wide unsigned long, is sufficient to handle the largest value of the bit shift expression:
size=0xffffffff nr_pages=100000
Modify round_pipe_size() to return 0 if n == 0 and updates its callers to handle accordingly.
Link: http://lkml.kernel.org/r/1507658689-11669-3-git-send-email-joe.lawrence@redh... Signed-off-by: Joe Lawrence joe.lawrence@redhat.com Reported-by: Mikulas Patocka mpatocka@redhat.com Reviewed-by: Mikulas Patocka mpatocka@redhat.com Cc: Al Viro viro@zeniv.linux.org.uk Cc: Jens Axboe axboe@kernel.dk Cc: Michael Kerrisk mtk.manpages@gmail.com Cc: Randy Dunlap rdunlap@infradead.org Cc: Josh Poimboeuf jpoimboe@redhat.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- fs/pipe.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-)
--- a/fs/pipe.c +++ b/fs/pipe.c @@ -1006,13 +1006,19 @@ const struct file_operations pipefifo_fo
/* * Currently we rely on the pipe array holding a power-of-2 number - * of pages. + * of pages. Returns 0 on error. */ static inline unsigned int round_pipe_size(unsigned int size) { unsigned long nr_pages;
+ if (size < pipe_min_size) + size = pipe_min_size; + nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT; + if (nr_pages == 0) + return 0; + return roundup_pow_of_two(nr_pages) << PAGE_SHIFT; }
@@ -1028,6 +1034,8 @@ static long pipe_set_size(struct pipe_in long ret = 0;
size = round_pipe_size(arg); + if (size == 0) + return -EINVAL; nr_pages = size >> PAGE_SHIFT;
if (!nr_pages) @@ -1110,13 +1118,18 @@ out_revert_acct: int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf, size_t *lenp, loff_t *ppos) { + unsigned int rounded_pipe_max_size; int ret;
ret = proc_dointvec_minmax(table, write, buf, lenp, ppos); if (ret < 0 || !write) return ret;
- pipe_max_size = round_pipe_size(pipe_max_size); + rounded_pipe_max_size = round_pipe_size(pipe_max_size); + if (rounded_pipe_max_size == 0) + return -EINVAL; + + pipe_max_size = rounded_pipe_max_size; return ret; }