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, loff_t offset, loff_t length, 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, loff_t offset, loff_t length, }
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;
if (flags & IOMAP_REPORT) { ret = ext4_map_blocks(NULL, inode, &map, 0);
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
On Fri, Aug 31, 2018 at 01:31:05PM -0600, Andreas Dilger wrote:
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".
first_block and last_block are both 32-bit values and defined as unsigned long. That's because they are logical block numbers and should never be more than 2**32. The fact that last_block had overflowed was due to i_size being corrupted to being an insanely large number.
So it's fine that len is an unsigned long, since first_block and last_block are both unsigned long.
- Ted
On 08/31/2018, 07:41 PM, Theodore Ts'o 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, loff_t offset, loff_t length, 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, loff_t offset, loff_t length, } 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;
Can't this be just
map.m_len = min_t(unsigned long, last_block - first_block + 1, UINT_MAX)?
if (flags & IOMAP_REPORT) { ret = ext4_map_blocks(NULL, inode, &map, 0);
thanks,
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)) {
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