CVE-2024-50265

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

ocfs2: remove entry once instead of null-ptr-dereference in ocfs2xaremove()

Syzkaller is able to provoke null-ptr-dereference in ocfs2xaremove():

[ 57.319872] (a.out,1161,7):ocfs2xaremove:2028 ERROR: status = -12 [ 57.320420] (a.out,1161,7):ocfs2xacleanupvaluetruncate:1999 ERROR: Partial truncate while removing xattr overlay.upper. Leaking 1 clusters and removing the entry [ 57.321727] BUG: kernel NULL pointer dereference, address: 0000000000000004 [...] [ 57.325727] RIP: 0010:ocfs2xablockwipenamevalue+0x2a/0xc0 [...] [ 57.331328] Call Trace: [ 57.331477] <TASK> [...] [ 57.333511] ? douseraddrfault+0x3e5/0x740 [ 57.333778] ? excpagefault+0x70/0x170 [ 57.334016] ? asmexcpagefault+0x2b/0x30 [ 57.334263] ? __pfxocfs2xablockwipenamevalue+0x10/0x10 [ 57.334596] ? ocfs2xablockwipenamevalue+0x2a/0xc0 [ 57.334913] ocfs2xaremoveentry+0x23/0xc0 [ 57.335164] ocfs2xaset+0x704/0xcf0 [ 57.335381] ? rawspinunlock+0x1a/0x40 [ 57.335620] ? ocfs2inodecacheunlock+0x16/0x20 [ 57.335915] ? tracepreempton+0x1e/0x70 [ 57.336153] ? startthishandle+0x16c/0x500 [ 57.336410] ? preemptcountsub+0x50/0x80 [ 57.336656] ? rawreadunlock+0x20/0x40 [ 57.336906] ? startthishandle+0x16c/0x500 [ 57.337162] ocfs2xattrblockset+0xa6/0x1e0 [ 57.337424] __ocfs2xattrsethandle+0x1fd/0x5d0 [ 57.337706] ? ocfs2starttrans+0x13d/0x290 [ 57.337971] ocfs2xattrset+0xb13/0xfb0 [ 57.338207] ? dput+0x46/0x1c0 [ 57.338393] ocfs2xattrtrustedset+0x28/0x30 [ 57.338665] ? ocfs2xattrtrusted_set+0x28/0x30 [ 57.338948] __vfs_removexattr+0x92/0xc0 [ 57.339182] _vfsremovexattrlocked+0xd5/0x190 [ 57.339456] ? preemptcountsub+0x50/0x80 [ 57.339705] vfsremovexattr+0x5f/0x100 [...]

Reproducer uses faultinject facility to fail ocfs2xaremove() -> ocfs2xavalue_truncate() with -ENOMEM.

In this case the comment mentions that we can return 0 if ocfs2xacleanupvaluetruncate() is going to wipe the entry anyway. But the following 'rc' check is wrong and execution flow do 'ocfs2xaremoveentry(loc);' twice: * 1st: in ocfs2xacleanupvaluetruncate(); * 2nd: returning back to ocfs2xa_remove() instead of going to 'out'.

Fix this by skipping the 2nd removal of the same entry and making syzkaller repro happy.