inet6_dump_fib() saves its progress in cb->args[1] as a positional
index within the current hash chain. Between batches, a concurrent
fib6_new_table() can insert a new table at the chain head, shifting
all existing entries. The saved index then lands on a different
table, causing fib6_dump_table() to set w->root to the wrong table
while w->node still points into the previous one.
fib6_walk_continue() dereferences w->node->parent (NULL) and panics:
BUG: kernel NULL pointer dereference, address: 0000000000000008
RIP: 0010:fib6_walk_continue+0x6e/0x170
Call Trace:
<TASK>
fib6_dump_table.isra.0+0xc5/0x240
inet6_dump_fib+0xf6/0x420
rtnl_dumpit+0x30/0xa0
netlink_dump+0x15b/0x460
netlink_recvmsg+0x1d6/0x2a0
____sys_recvmsg+0x17a/0x190
Fix by storing tb->tb6_id in cb->args[1] instead of a positional
index. On resume, skip entries until the id matches; a concurrent
head-insert can never match the saved id, so the walker always
resumes on the correct table.
Fixes: 1b43af5480 ("[IPV6]: Increase number of possible routing tables to 2^32")
Signed-off-by: Pengfei Zhang <zhangfeionline@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260625070517.965597-1-zhangfeionline@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
9facb861dc