In the Linux kernel, the following vulnerability has been resolved:

gfs2: Fix use-after-free in iomap inline data write path

The inline data buffer head (dibh) is being released prematurely in gfs2iomapbegin() via releasemetapath() while iomap->inlinedata still points to dibh->bdata. This causes a use-after-free when iomapwriteendinline() later attempts to write to the inline data area.

The bug sequence: 1. gfs2iomapbegin() calls gfs2metainodebuffer() to read inode metadata into dibh 2. Sets iomap->inlinedata = dibh->bdata + sizeof(struct gfs2dinode) 3. Calls releasemetapath() which calls brelse(dibh), dropping refcount to 0 4. kswapd reclaims the page (~39ms later in the syzbot report) 5. iomapwriteendinline() tries to memcpy() to iomap->inlinedata 6. KASAN detects use-after-free write to freed memory

Fix by storing dibh in iomap->private and incrementing its refcount with getbh() in gfs2iomapbegin(). The buffer is then properly released in gfs2iomapend() 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 gfs2iomapbegin() to avoid leaks in gfs2iomapget() and gfs2iomapalloc().]