** Tags removed: verification-needed-bionic ** Tags added: bionic verification-done-bionic
-- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1934175 Title: Kernel oops due to uninitialized list on kernfs (kernfs_kill_sb) Status in linux package in Ubuntu: In Progress Status in linux source package in Bionic: Fix Committed Bug description: [Impact] * We had a recent report of a kernel crash due to a NULL pointer dereference in a Bionic 4.15 derivative kernel, as per the following log collected: [...] [537105.767348] SLUB: Unable to allocate memory on node -1, gfp=0x14000c0(GFP_KERNEL) [...] [537105.767368] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 [537105.777711] IP: kernfs_kill_sb+0x31/0x70 [537105.783582] PGD 0 P4D 0 [537105.787844] Oops: 0002 [#1] SMP PTI [...] RIP: 0010:kernfs_kill_sb+0x31/0x70 RSP: 0018:ffffb90aec1afd00 EFLAGS: 00010286 RAX: 0000000000000000 RBX: ffff9fdbd567d900 RCX: ffffa0143885ae01 RDX: 0000000000000000 RSI: ffffa0143885ae00 RDI: ffffffffa2937c40 RBP: ffffb90aec1afd10 R08: ffffa0150b581510 R09: 000000018100004d R10: ffffb90aec1afcd8 R11: 0000000000000100 R12: ffffa01436e43000 R13: ffffa01436e43000 R14: 0000000000000000 R15: ffff9fdbd567d900 FS: 00007fe41a615b80(0000) GS:ffffa01afea40000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000008 CR3: 0000007dfe3cc003 CR4: 00000000003606e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: sysfs_kill_sb+0x1f/0x40 deactivate_locked_super+0x48/0x80 kernfs_mount_ns+0x1eb/0x230 sysfs_mount+0x66/0xc0 mount_fs+0x37/0x160 ? alloc_vfsmnt+0x1b3/0x230 vfs_kern_mount.part.24+0x5d/0x110 do_mount+0x5ed/0xce0 [...] * The following detailed call stack plus the disassembly help to understand the cause of the issue: mount_fs() --sysfs_mount() ----kernfs_mount_ns() <inlined kernfs_fill_super() fails, very likely due to being unable to allocate memory> ------deactivate_locked_super() <given the callback .kill_sb = sysfs_kill_sb, next function is called> --------sysfs_kill_sb() ----------kernfs_kill_sb() <OOPS due to the unitialized list> The below disassembly of kernfs_kill_sb() clarifies exactly the issue: ffffffff812f46e0 <kernfs_kill_sb>: [ ... prologue ...] 48 8b 9f 08 04 00 00 mov 0x408(%rdi),%rbx # %rbx = kernfs_super_info *info = sb->s_fs_info 49 89 fc mov %rdi,%r12 # %r12 = super_block *sb 48 c7 c7 40 7c 53 82 mov $0xffffffff82537c40,%rdi # %rdi = &kernfs_mutex (global) ffffffff812f46f9: R_X86_64_32S kernfs_mutex e8 ee da 67 00 callq ffffffff819721f0 <mutex_lock> # mutex_lock(&kernfs_mutex); [...] 48 8b 53 18 mov 0x18(%rbx),%rdx # %rdx = info->node 48 8b 43 20 mov 0x20(%rbx),%rax # based on splat, RAX == 0x0 [info->head.prev] 48 89 42 08 mov %rax,0x8(%rdx) # <- OOPS [tried to assign next->prev = prev, see __list_del()] 48 89 10 mov %rdx,(%rax) 48 b8 00 01 00 00 00 movabs $0xdead000000000100,%rax # node->next = LIST_POISON1 [...] * The fix for this issue comes from upstream commit 82382acec0c9 ("kernfs: deal with kernfs_fill_super() failures"); this commit is a very trivial fix that adds an INIT_LIST_HEAD(&info->node) in kernfs_mount_ns(), making the list prev/next pointers valid since the beginning. Unfortunately this commit wasn't CCed to stable email when sent, so it wasn't automatically picked up by Ubuntu kernel; now it was properly submitted to stable list [0]. * Along with this fix, we found another commit (7b745a4e4051) which is a small/simple fix to correlated code, that also should have been sent to 4.14.y stable branch, but for some reason wasn't. Since both commits were accepted in linux-stable, we are hereby proposing the backport for Ubuntu kernel 4.15. [0] https://lore.kernel.org/stable/20210622210622.9925-1-gpicc...@canonical.com/ [Test Case] * We don't have a real test case, although low-memory condition or an artificial kprobe reproducer could easily trigger the issue. * We booted a qemu virtual machine with a kernel containing both patches with no issues. [Where problems could occur] * The likelihood of issues are low, specially due to the fact both patches are very simple and they are on upstream kernel for more than 3 years (and were quickly accepted in 4.14.y stable branch last week). * With that sad, the second patch could potentially introduce issues with super_block references - I honestly cannot conceive any issues potentially caused by patch 1. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1934175/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp