slub: Handle NULL parameter in kmem_cache_flags

[Linux-MTD Mailing List]

Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=c6f58d9b362b45c52afebe4342c9137d0dabe47f
Commit:     c6f58d9b362b45c52afebe4342c9137d0dabe47f
Parent:     ea982d9ffdfaa22552e9b0b9be94f459afa36102
Author:     Christoph Lameter <cl at linux.com>
AuthorDate: Thu Nov 7 16:29:15 2013 +0000
Committer:  Pekka Enberg <penberg at kernel.org>
CommitDate: Mon Nov 11 18:15:45 2013 +0200

    slub: Handle NULL parameter in kmem_cache_flags
    
    Andreas Herrmann writes:
    
      When I've used slub_debug kernel option (e.g.
      "slub_debug=,skbuff_fclone_cache" or similar) on a debug session I've
      seen a panic like:
    
        Highbank #setenv bootargs console=ttyAMA0 root=/dev/sda2 kgdboc.kgdboc=ttyAMA0,115200 slub_debug=,kmalloc-4096 earlyprintk=ttyAMA0
        ...
        Unable to handle kernel NULL pointer dereference at virtual address 00000000
        pgd = c0004000
        [00000000] *pgd=00000000
        Internal error: Oops: 5 [#1] SMP ARM
        Modules linked in:
        CPU: 0 PID: 0 Comm: swapper Tainted: G        W    3.12.0-00048-gbe408cd #314
        task: c0898360 ti: c088a000 task.ti: c088a000
        PC is at strncmp+0x1c/0x84
        LR is at kmem_cache_flags.isra.46.part.47+0x44/0x60
        pc : [<c02c6da0>]    lr : [<c0110a3c>]    psr: 200001d3
        sp : c088bea8  ip : c088beb8  fp : c088beb4
        r10: 00000000  r9 : 413fc090  r8 : 00000001
        r7 : 00000000  r6 : c2984a08  r5 : c0966e78  r4 : 00000000
        r3 : 0000006b  r2 : 0000000c  r1 : 00000000  r0 : c2984a08
        Flags: nzCv  IRQs off  FIQs off  Mode SVC_32  ISA ARM  Segment kernel
        Control: 10c5387d  Table: 0000404a  DAC: 00000015
        Process swapper (pid: 0, stack limit = 0xc088a248)
        Stack: (0xc088bea8 to 0xc088c000)
        bea0:                   c088bed4 c088beb8 c0110a3c c02c6d90 c0966e78 00000040
        bec0: ef001f00 00000040 c088bf14 c088bed8 c0112070 c0110a04 00000005 c010fac8
        bee0: c088bf5c c088bef0 c010fac8 ef001f00 00000040 00000000 00000040 00000001
        bf00: 413fc090 00000000 c088bf34 c088bf18 c0839190 c0112040 00000000 ef001f00
        bf20: 00000000 00000000 c088bf54 c088bf38 c0839200 c083914c 00000006 c0961c4c
        bf40: c0961c28 00000000 c088bf7c c088bf58 c08392ac c08391c0 c08a2ed8 c0966e78
        bf60: c086b874 c08a3f50 c0961c28 00000001 c088bfb4 c088bf80 c083b258 c0839248
        bf80: 2f800000 0f000000 c08935b4 ffffffff c08cd400 ffffffff c08cd400 c0868408
        bfa0: c29849c0 00000000 c088bff4 c088bfb8 c0824974 c083b1e4 ffffffff ffffffff
        bfc0: c08245c0 00000000 00000000 c0868408 00000000 10c5387d c0892bcc c0868404
        bfe0: c0899440 0000406a 00000000 c088bff8 00008074 c0824824 00000000 00000000
        [<c02c6da0>] (strncmp+0x1c/0x84) from [<c0110a3c>] (kmem_cache_flags.isra.46.part.47+0x44/0x60)
        [<c0110a3c>] (kmem_cache_flags.isra.46.part.47+0x44/0x60) from [<c0112070>] (__kmem_cache_create+0x3c/0x410)
        [<c0112070>] (__kmem_cache_create+0x3c/0x410) from [<c0839190>] (create_boot_cache+0x50/0x74)
        [<c0839190>] (create_boot_cache+0x50/0x74) from [<c0839200>] (create_kmalloc_cache+0x4c/0x88)
        [<c0839200>] (create_kmalloc_cache+0x4c/0x88) from [<c08392ac>] (create_kmalloc_caches+0x70/0x114)
        [<c08392ac>] (create_kmalloc_caches+0x70/0x114) from [<c083b258>] (kmem_cache_init+0x80/0xe0)
        [<c083b258>] (kmem_cache_init+0x80/0xe0) from [<c0824974>] (start_kernel+0x15c/0x318)
        [<c0824974>] (start_kernel+0x15c/0x318) from [<00008074>] (0x8074)
        Code: e3520000 01a00002 089da800 e5d03000 (e5d1c000)
        ---[ end trace 1b75b31a2719ed1d ]---
        Kernel panic - not syncing: Fatal exception
    
      Problem is that slub_debug option is not parsed before
      create_boot_cache is called. Solve this by changing slub_debug to
      early_param.
    
      Kernels 3.11, 3.10 are also affected.  I am not sure about older
      kernels.
    
    Christoph Lameter explains:
    
      kmem_cache_flags may be called with NULL parameter during early boot.
      Skip the test in that case.
    
    Cc: stable at vger.kernel.org # 3.10 and 3.11
    Reported-by: Andreas Herrmann <andreas.herrmann at calxeda.com>
    Signed-off-by: Christoph Lameter <cl at linux.com>
    Signed-off-by: Pekka Enberg <penberg at kernel.org>
---
 mm/slub.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 250062c..2cf3982 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1220,8 +1220,8 @@ static unsigned long kmem_cache_flags(unsigned long object_size,
 	/*
 	 * Enable debugging if selected on the kernel commandline.
 	 */
-	if (slub_debug && (!slub_debug_slabs ||
-		!strncmp(slub_debug_slabs, name, strlen(slub_debug_slabs))))
+	if (slub_debug && (!slub_debug_slabs || (name &&
+		!strncmp(slub_debug_slabs, name, strlen(slub_debug_slabs)))))
 		flags |= slub_debug;
 
 	return flags;