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| author | Chen Jun <chenjun102@huawei.com> | 2019-12-01 04:58:11 +0300 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-12-01 23:59:10 +0300 |
| commit | aa71ecd8d86500da6081a72da6b0b524007e0627 (patch) | |
| tree | eb0b72deeff9fa3e25e8b10996d223f8aee285b4 /mm | |
| parent | 4afab1cd256e425803374b58702ea86a05b0acf9 (diff) | |
| download | linux-aa71ecd8d86500da6081a72da6b0b524007e0627.tar.xz | |
mm/shmem.c: cast the type of unmap_start to u64
In 64bit system. sb->s_maxbytes of shmem filesystem is MAX_LFS_FILESIZE,
which equal LLONG_MAX.
If offset > LLONG_MAX - PAGE_SIZE, offset + len < LLONG_MAX in
shmem_fallocate, which will pass the checking in vfs_fallocate.
/* Check for wrap through zero too */
if (((offset + len) > inode->i_sb->s_maxbytes) || ((offset + len) < 0))
return -EFBIG;
loff_t unmap_start = round_up(offset, PAGE_SIZE) in shmem_fallocate
causes a overflow.
Syzkaller reports a overflow problem in mm/shmem:
UBSAN: Undefined behaviour in mm/shmem.c:2014:10
signed integer overflow: '9223372036854775807 + 1' cannot be represented in type 'long long int'
CPU: 0 PID:17076 Comm: syz-executor0 Not tainted 4.1.46+ #1
Hardware name: linux, dummy-virt (DT)
Call trace:
dump_backtrace+0x0/0x2c8 arch/arm64/kernel/traps.c:100
show_stack+0x20/0x30 arch/arm64/kernel/traps.c:238
__dump_stack lib/dump_stack.c:15 [inline]
ubsan_epilogue+0x18/0x70 lib/ubsan.c:164
handle_overflow+0x158/0x1b0 lib/ubsan.c:195
shmem_fallocate+0x6d0/0x820 mm/shmem.c:2104
vfs_fallocate+0x238/0x428 fs/open.c:312
SYSC_fallocate fs/open.c:335 [inline]
SyS_fallocate+0x54/0xc8 fs/open.c:239
The highest bit of unmap_start will be appended with sign bit 1
(overflow) when calculate shmem_falloc.start:
shmem_falloc.start = unmap_start >> PAGE_SHIFT.
Fix it by casting the type of unmap_start to u64, when right shifted.
This bug is found in LTS Linux 4.1. It also seems to exist in mainline.
Link: http://lkml.kernel.org/r/1573867464-5107-1-git-send-email-chenjun102@huawei.com
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/shmem.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/shmem.c b/mm/shmem.c index 3c336b02cf08..165fa6332993 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2747,7 +2747,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset, } shmem_falloc.waitq = &shmem_falloc_waitq; - shmem_falloc.start = unmap_start >> PAGE_SHIFT; + shmem_falloc.start = (u64)unmap_start >> PAGE_SHIFT; shmem_falloc.next = (unmap_end + 1) >> PAGE_SHIFT; spin_lock(&inode->i_lock); inode->i_private = &shmem_falloc; |