erofs/zmap.c: Fix incorrect offset calculation
PATCH v2 1/1 erofs/zmap.c: Fix incorrect offset calculation
Effective offset to add to length was being incorrectly calculated, which resulted in iomap->length being set to 0, triggering a WARN_ON in iomap_iter_done().
Fix that, and describe it in comments.
This was reported as a crash by syzbot under an issue about a warning encountered in iomap_iter_done(), but unrelated to erofs.
C reproducer: https://syzkaller.appspot.com/text?tag=ReproC&x=1037a6b2880000
Kernel config: https://syzkaller.appspot.com/text?tag=KernelConfig&x=e2021a61197ebe02
Dashboard link: https://syzkaller.appspot.com/bug?extid=a8e049cd3abd342936b6
---
Changes since v2:
- Fix the calculation instead of bailing out.
fs/erofs/zmap.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
fs/erofs/zmap.c +7 -3
@@ -790,12 +790,16 @@ static int z_erofs_iomap_begin_report(struct inode *inode, loff_t offset, iomap->type =IOMAP_HOLE ; iomap->addr =IOMAP_NULL_ADDR ;/* -* No strict rule how to describe extents for post EOF, yet -* we need do like below. Otherwise, iomap itself will get +* No strict rule on how to describe extents for post EOF, yet +* we need to do like below. Otherwise, iomap itself will get * into an endless loop on post EOF. +* +* Calculate the effective offset by subtracting extent start +* (map.m_la) from the requested offset, and add it to length. +* (NB: offset >= map.m_la always) */ if (iomap->offset >= inode->i_size) - iomap->length = length + map.m_la - offset; + iomap->length = length + offset - map.m_la; } iomap->flags =0 ;return 0 ;
Signature · 1 line
2.35.1
Quoted 9 lines · Siddh Raman Pant via Linux-erofs
Effective offset to add to length was being incorrectly calculated, which resulted in
iomap->lengthbeing set to 0, triggering aWARN_ONiniomap_iter_done().Fix that, and describe it in comments.
This was reported as a crash by syzbot under an issue about a warning encountered in
iomap_iter_done(), but unrelated to erofs.
Quoted 7 lines
C reproducer: https://syzkaller.appspot.com/text?tag=ReproC&x=1037a6b2880000
Kernel config: https://syzkaller.appspot.com/text?tag=KernelConfig&x=e2021a61197ebe02
Dashboard link: https://syzkaller.appspot.com/bug?extid=a8e049cd3abd342936b6Reported-by [email protected]Suggested-by Gao Xiang <[email protected]>Signed-off-by Siddh Raman Pant <[email protected]>
It looks good to me!
Thanks,
Gao Xiang
Quoted 35 lines
---
Changes since v2:
- Fix the calculation instead of bailing out.fs/erofs/zmap.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)fs/erofs/zmap.c +7
-3@@ -790,12 +790,16 @@ static int z_erofs_iomap_begin_report(struct inode *inode, loff_t offset, iomap->type =IOMAP_HOLE ; iomap->addr =IOMAP_NULL_ADDR ;/* -* No strict rule how to describe extents for post EOF, yet -* we need do like below. Otherwise, iomap itself will get +* No strict rule on how to describe extents for post EOF, yet +* we need to do like below. Otherwise, iomap itself will get * into an endless loop on post EOF. +* +* Calculate the effective offset by subtracting extent start +* (map.m_la) from the requested offset, and add it to length. +* (NB: offset >= map.m_la always) */ if (iomap->offset >= inode->i_size) - iomap->length = length + map.m_la - offset; + iomap->length = length + offset - map.m_la; } iomap->flags =0 ;return 0 ;Signature · 1 line
2.35.1
Quoted 9 lines · Siddh Raman Pant
Effective offset to add to length was being incorrectly calculated, which resulted in
iomap->lengthbeing set to 0, triggering aWARN_ONiniomap_iter_done().Fix that, and describe it in comments.
This was reported as a crash by syzbot under an issue about a warning encountered in
iomap_iter_done(), but unrelated to erofs.
Quoted 7 lines
C reproducer: https://syzkaller.appspot.com/text?tag=ReproC&x=1037a6b2880000
Kernel config: https://syzkaller.appspot.com/text?tag=KernelConfig&x=e2021a61197ebe02
Dashboard link: https://syzkaller.appspot.com/bug?extid=a8e049cd3abd342936b6Reported-by [email protected]Suggested-by Gao Xiang <[email protected]>Signed-off-by Siddh Raman Pant <[email protected]>
Thanks,