| Message ID | 20180831174126.13071-1-tytso@mit.edu |
|---|---|
| State | Superseded |
| Headers | show |
| Series | ext4: avoid arithemetic overflow that can trigger a BUG | expand |
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 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,
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 Fri, Aug 31, 2018 at 09:31:36PM +0200, Jiri Slaby wrote: > > Can't this be just > > map.m_len = min_t(unsigned long, last_block - first_block + 1, UINT_MAX)? Yes, good point, thanks. - Ted
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);
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(-)