diff options
| author | Deepanshu Kartikey <kartikey406@gmail.com> | 2026-01-30 14:51:34 +0530 |
|---|---|---|
| committer | Andreas Gruenbacher <agruenba@redhat.com> | 2026-01-30 13:21:57 +0100 |
| commit | faddeb848305e79db89ee0479bb0e33380656321 (patch) | |
| tree | 0416078ba2e0a77c397e08afabe55c3f213a1dc2 | |
| parent | 22150a7d401d9e9169b9b68e05bed95f7f49bf69 (diff) | |
gfs2: Fix use-after-free in iomap inline data write path
The inline data buffer head (dibh) is being released prematurely in
gfs2_iomap_begin() via release_metapath() while iomap->inline_data
still points to dibh->b_data. This causes a use-after-free when
iomap_write_end_inline() later attempts to write to the inline data
area.
The bug sequence:
1. gfs2_iomap_begin() calls gfs2_meta_inode_buffer() to read inode
metadata into dibh
2. Sets iomap->inline_data = dibh->b_data + sizeof(struct gfs2_dinode)
3. Calls release_metapath() which calls brelse(dibh), dropping refcount
to 0
4. kswapd reclaims the page (~39ms later in the syzbot report)
5. iomap_write_end_inline() tries to memcpy() to iomap->inline_data
6. KASAN detects use-after-free write to freed memory
Fix by storing dibh in iomap->private and incrementing its refcount
with get_bh() in gfs2_iomap_begin(). The buffer is then properly
released in gfs2_iomap_end() after the inline write completes,
ensuring the page stays alive for the entire iomap operation.
Note: A C reproducer is not available for this issue. The fix is based
on analysis of the KASAN report and code review showing the buffer head
is freed before use.
[agruenba: Take buffer head reference in gfs2_iomap_begin() to avoid
leaks in gfs2_iomap_get() and gfs2_iomap_alloc().]
Reported-by: syzbot+ea1cd4aa4d1e98458a55@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ea1cd4aa4d1e98458a55
Fixes: d0a22a4b03b8 ("gfs2: Fix iomap write page reclaim deadlock")
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
| -rw-r--r-- | fs/gfs2/bmap.c | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/fs/gfs2/bmap.c b/fs/gfs2/bmap.c index 131091520de6..fdcac8e3f2ba 100644 --- a/fs/gfs2/bmap.c +++ b/fs/gfs2/bmap.c @@ -1127,10 +1127,18 @@ static int gfs2_iomap_begin(struct inode *inode, loff_t pos, loff_t length, goto out_unlock; break; default: - goto out_unlock; + goto out; } ret = gfs2_iomap_begin_write(inode, pos, length, flags, iomap, &mp); + if (ret) + goto out_unlock; + +out: + if (iomap->type == IOMAP_INLINE) { + iomap->private = metapath_dibh(&mp); + get_bh(iomap->private); + } out_unlock: release_metapath(&mp); @@ -1144,6 +1152,9 @@ static int gfs2_iomap_end(struct inode *inode, loff_t pos, loff_t length, struct gfs2_inode *ip = GFS2_I(inode); struct gfs2_sbd *sdp = GFS2_SB(inode); + if (iomap->private) + brelse(iomap->private); + switch (flags & (IOMAP_WRITE | IOMAP_ZERO)) { case IOMAP_WRITE: if (flags & IOMAP_DIRECT) |