gfs2: Fix kernel NULL pointer dereference in gfs2rgrpdump

Syzkaller has reported a NULL pointer dereference when accessing rgd->rdrgl in gfs2rgrpdump(). This can happen when creatingrgd->rdgl fails in readrindexentry(). Add a NULL pointer check in gfs2rgrpdump() to prevent that.

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

gfs2: prevent NULL pointer dereference during unmount

When flushing out outstanding glock work during an unmount, gfs2logflush() can be called when sdp->sdjdesc has already been deallocated and sdp->sdjdesc is NULL. Commit 35264909e9d1 ("gfs2: Fix NULL pointer dereference in gfs2logflush") added a check for that to gfs2logflush() itself, but it missed the sdp->sdjdesc dereference in gfs2logrelease(). Fix that.

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

gfs2: fiemap page fault fix

In gfs2fiemap(), we are calling iomapfiemap() while holding the inode glock. This can lead to recursive glock taking if the fiemap buffer is memory mapped to the same inode and accessing it triggers a page fault.

Fix by disabling page faults for iomapfiemap() and faulting in the buffer by hand if necessary.

Fixes xfstest generic/742.