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

net: core: remove unnecessary frame_sz check in bpf_xdp_adjust_tail()

Syzkaller reported the following issue:

Too BIG xdp->frame_sz = 131072 WARNING: CPU: 0 PID: 5020 at net/core/filter.c:4121 ____bpf_xdp_adjust_tail net/core/filter.c:4121 [inline] WARNING: CPU: 0 PID: 5020 at net/core/filter.c:4121 bpf_xdp_adjust_tail+0x466/0xa10 net/core/filter.c:4103 … Call Trace: bpf_prog_4add87e5301a4105+0x1a/0x1c __bpf_prog_run include/linux/filter.h:600 [inline] bpf_prog_run_xdp include/linux/filter.h:775 [inline] bpf_prog_run_generic_xdp+0x57e/0x11e0 net/core/dev.c:4721 netif_receive_generic_xdp net/core/dev.c:4807 [inline] do_xdp_generic+0x35c/0x770 net/core/dev.c:4866 tun_get_user+0x2340/0x3ca0 drivers/net/tun.c:1919 tun_chr_write_iter+0xe8/0x210 drivers/net/tun.c:2043 call_write_iter include/linux/fs.h:1871 [inline] new_sync_write fs/read_write.c:491 [inline] vfs_write+0x650/0xe40 fs/read_write.c:584 ksys_write+0x12f/0x250 fs/read_write.c:637 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd

xdp->frame_sz > PAGE_SIZE check was introduced in commit c8741e2bfe87 (xdp: Allow bpf_xdp_adjust_tail() to grow packet size). But Jesper Dangaard Brouer jbrouer@redhat.com noted that after introducing the xdp_init_buff() which all XDP driver use - its safe to remove this check. The original intend was to catch cases where XDP drivers have not been updated to use xdp.frame_sz, but that is not longer a concern (since xdp_init_buff).

Running the initial syzkaller repro it was discovered that the contiguous physical memory allocation is used for both xdp paths in tun_get_user(), e.g. tun_build_skb() and tun_alloc_skb(). It was also stated by Jesper Dangaard Brouer jbrouer@redhat.com that XDP can work on higher order pages, as long as this is contiguous physical memory (e.g. a page).

Affected Software

References

• https://git.kernel.org/stable/c/20acffcdc2b74fb7dcc4e299f7aca173df89d911
• https://git.kernel.org/stable/c/a09c258cfa77d3ba0a7acc555c73eb6b005c4bd8
• https://git.kernel.org/stable/c/d14eea09edf427fa36bd446f4a3271f99164202f
• https://git.kernel.org/stable/c/d9252d67ed2f921c230bba449ee051b5c32e4841