Hi all,
I just hit a boot crash on v6.7-rc2 (arm64, FVP model):
[ 1.418845] Unable to handle kernel NULL pointer dereference at virtual
address 0000000000000517
[ 1.418855] Mem abort info:
[ 1.418860] ESR = 0x0000000096000004
[ 1.418867] EC = 0x25: DABT (current EL), IL = 32 bits
[ 1.418876] SET = 0, FnV = 0
[ 1.418882] EA = 0, S1PTW = 0
[ 1.418889] FSC = 0x04: level 0 translation fault
[ 1.418897] Data abort info:
[ 1.418902] ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
[ 1.418910] CM = 0, WnR = 0, TnD = 0, TagAccess = 0
[ 1.418919] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[ 1.418928] user pgtable: 4k pages, 48-bit VAs, pgdp=0000000881835000
[ 1.418938] [0000000000000517] pgd=0000000000000000, p4d=0000000000000000
[ 1.418952] Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
[ 1.418961] Modules linked in:
[ 1.418969] CPU: 0 PID: 8 Comm: kworker/0:0 Tainted: G T
6.7.0-rc2-dirty #4191 40d10cdc812c74fd5dc5d91e2452ff6f1e5f4b4a
[ 1.418984] Hardware name: FVP Base RevC (DT)
[ 1.418992] Workqueue: mld mld_ifc_work
[ 1.419003] pstate: 101402005 (nzcv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
[ 1.419016] pc : ___neigh_create+0x790/0x9c8
[ 1.419028] lr : ___neigh_create+0x270/0x9c8
[ 1.419041] sp : ffff8000800c3a20
[ 1.419048] x29: ffff8000800c3a20 x28: ffffd7c64c921078 x27: ffff00080188bd50
[ 1.419066] x26: ffff00080183a30c x25: ffff00080188bda0 x24: ffff00080183a300
[ 1.419084] x23: 0000000000000000 x22: 0000000000000010 x21: ffff00080188bcc0
[ 1.419102] x20: 0000000000000000 x19: ffff0008003ef000 x18: 0000000000000014
[ 1.419119] x17: 00000000cf0f2572 x16: 0000000080faa78d x15: 00000000b79921ac
[ 1.419137] x14: ffff00087ff332c0 x13: 1600000000000000 x12: 00000000000002ff
[ 1.419155] x11: 000000007c2c4dbd x10: 0000000000000003 x9 : 0000000000000000
[ 1.419172] x8 : ffff00080188bd80 x7 : 00000000be3df655 x6 : 00000000f1691d6f
[ 1.419190] x5 : 000000007c2c4dbd x4 : 0000000000000000 x3 : 000000008eb8ab5b
[ 1.419207] x2 : 000000000000050f x1 : 000000000000001d x0 : 00000000000002ff
[ 1.419225] Call trace:
[ 1.419230] ___neigh_create+0x790/0x9c8
[ 1.419243] __neigh_create+0x18/0x20
[ 1.419255] ip6_finish_output2+0x5f8/0x8c4
[ 1.419267] ip6_finish_output+0x1f0/0x258
[ 1.419279] ip6_output+0x70/0x1cc
[ 1.419291] NF_HOOK.constprop.0+0x4c/0xd8
[ 1.419302] mld_sendpack+0x1b4/0x394
[ 1.419313] mld_ifc_work+0x1d4/0x4b4
I tracked it down to the following line in net/core/neighbour.c ___neigh_create:
memcpy(n->primary_key, pkey, key_len);
I did this by surrounding the memcpy with BUG():
BUG_ON(n->tbl != tbl);
memcpy(n->primary_key, pkey, key_len);
BUG_ON(n->tbl != tbl);
And it was crashing on the second one.
Checking `struct neighbour`:
struct neighbour {
struct neighbour __rcu *next;
struct neigh_table *tbl;
.. fields ..
u8 primary_key[0];
} __randomize_layout;
Due to the `__randomize_layout`, `primary_key` field is being placed before
`tbl` (actually it's the same address since it's a 0 length array). That means
the memcpy() corrupts the tbl pointer.
I think I just got unlucky with my CONFIG_RANDSTRUCT seed (I can provide it if
needed), it doesn't look as if it's a new issue.
I couldn't reproduce directly on v6.6 (the offsets for `tbl` and `primary_key`
didn't overlap).
However I tried changing the zero-length-array to a flexible one:
+ DECLARE_FLEX_ARRAY(u8, primary_key);
+ u8 primary_key[0];
Then the field offsets ended up overlapping, and I also got the same crash on
v6.6.
Thanks,
Joey
