On Aug 31, 2018, at 11:41 AM, Theodore Ts'o tytso@mit.edu wrote:

A maliciously crafted file system can cause an overflow when the results of a 64-bit calculation is stored into a 32-bit length parameter.

https://bugzilla.kernel.org/show_bug.cgi?id=200623

Signed-off-by: Theodore Ts'o tytso@mit.edu Reported-by: Wen Xu wen.xu@gatech.edu Cc: stable@vger.kernel.org

---

fs/ext4/inode.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 8f6ad7667974..1134c3473673 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -3414,6 +3414,7 @@ static int ext4_iomap_begin(struct inode *inode, unsigned int blkbits = inode->i_blkbits; unsigned long first_block = offset >> blkbits; unsigned long last_block = (offset + length - 1) >> blkbits;

• unsigned long len; struct ext4_map_blocks map; bool delalloc = false; int ret;

@@ -3434,7 +3435,8 @@ static int ext4_iomap_begin(struct inode *inode, }

map.m_lblk = first_block;

• map.m_len = last_block - first_block + 1;

• len = last_block - first_block + 1;
• map.m_len = (len < UINT_MAX) ? len : UINT_MAX;

Wouldn't "(len < UINT_MAX)" always be true on a 32-bit system, or is there some other limitation in that case (e.g. filesystem < 16TB) that prevents it from being an issue? Otherwise, this should use "unsigned long long len".

Cheers, Andreas

A maliciously crafted file system can cause an overflow when the results of a 64-bit calculation is stored into a 32-bit length parameter.

https://bugzilla.kernel.org/show_bug.cgi?id=200623

Signed-off-by: Theodore Ts'o tytso@mit.edu Reported-by: Wen Xu wen.xu@gatech.edu Cc: stable@vger.kernel.org --- This is a revised version which checks for overflows when caluclating first_block and last_block. This catches more overflow scenarios than just checking for an overflow when calculating map.m_len.

fs/ext4/ext4.h | 3 +++ fs/ext4/inode.c | 8 ++++++-- 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 249bcee4d7b2..ac05bd86643a 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -686,6 +686,9 @@ enum { /* Max physical block we can address w/o extents */ #define EXT4_MAX_BLOCK_FILE_PHYS 0xFFFFFFFF

+/* Max logical block we can support */ +#define EXT4_MAX_LOGICAL_BLOCK 0xFFFFFFFF + /* * Structure of an inode on the disk */ diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 8f6ad7667974..694f31364206 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -3412,12 +3412,16 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length, { struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb); unsigned int blkbits = inode->i_blkbits; - unsigned long first_block = offset >> blkbits; - unsigned long last_block = (offset + length - 1) >> blkbits; + unsigned long first_block, last_block; struct ext4_map_blocks map; bool delalloc = false; int ret;

+ if ((offset >> blkbits) > EXT4_MAX_LOGICAL_BLOCK) + return -EINVAL; + first_block = offset >> blkbits; + last_block = min_t(loff_t, (offset + length - 1) >> blkbits, + EXT4_MAX_LOGICAL_BLOCK);

if (flags & IOMAP_REPORT) { if (ext4_has_inline_data(inode)) {