Messages in this thread Patch in this message | | | From | Joe Lawrence <> | Subject | [PATCH 2/3] pipe: avoid round_pipe_size() nr_pages overflow on 32-bit | Date | Tue, 26 Sep 2017 10:21:23 -0400 |
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The round_pipe_size() function 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.
Reported-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com> --- fs/pipe.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/fs/pipe.c b/fs/pipe.c index a21ad26de557..8cbc97d97753 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -1017,13 +1017,19 @@ static int fifo_open(struct inode *inode, struct file *filp) /* * 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; } @@ -1039,6 +1045,8 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg) long ret = 0; size = round_pipe_size(arg); + if (size == 0) + return -EINVAL; nr_pages = size >> PAGE_SHIFT; if (!nr_pages) @@ -1122,13 +1130,18 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg) 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_douintvec_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; } -- 1.8.3.1
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