On Wed, Jun 29, 2022 at 09:30:12AM -0700, Axel Rasmussen wrote: > On Tue, Jun 28, 2022 at 9:41 PM Eric Biggers <ebiggers@xxxxxxxxxx> wrote: > > > > On Tue, Jun 28, 2022 at 03:59:26PM -0700, syzbot wrote: > > > Hello, > > > > > > syzbot found the following issue on: > > > > > > HEAD commit: 941e3e791269 Merge tag 'for_linus' of git://git.kernel.org.. > > > git tree: upstream > > > console+strace: https://syzkaller.appspot.com/x/log.txt?x=1670ded4080000 > > > kernel config: https://syzkaller.appspot.com/x/.config?x=833001d0819ddbc9 > > > dashboard link: https://syzkaller.appspot.com/bug?extid=9bd2b7adbd34b30b87e4 > > > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=140f9ba8080000 > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15495188080000 > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > > Reported-by: syzbot+9bd2b7adbd34b30b87e4@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > BUG: unable to handle page fault for address: ffff888021f7e005 > > > #PF: supervisor write access in kernel mode > > > #PF: error_code(0x0002) - not-present page > > > PGD 11401067 P4D 11401067 PUD 11402067 PMD 21f7d063 PTE 800fffffde081060 > > > Oops: 0002 [#1] PREEMPT SMP KASAN > > > CPU: 0 PID: 3761 Comm: syz-executor281 Not tainted 5.19.0-rc4-syzkaller-00014-g941e3e791269 #0 > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > > RIP: 0010:memset_erms+0x9/0x10 arch/x86/lib/memset_64.S:64 > > > Code: c1 e9 03 40 0f b6 f6 48 b8 01 01 01 01 01 01 01 01 48 0f af c6 f3 48 ab 89 d1 f3 aa 4c 89 c8 c3 90 49 89 f9 40 88 f0 48 89 d1 <f3> aa 4c 89 c8 c3 90 49 89 fa 40 0f b6 ce 48 b8 01 01 01 01 01 01 > > > RSP: 0018:ffffc9000329fa90 EFLAGS: 00010202 > > > RAX: 0000000000000000 RBX: 0000000000001000 RCX: 0000000000000ffb > > > RDX: 0000000000000ffb RSI: 0000000000000000 RDI: ffff888021f7e005 > > > RBP: ffffea000087df80 R08: 0000000000000001 R09: ffff888021f7e005 > > > R10: ffffed10043efdff R11: 0000000000000000 R12: 0000000000000005 > > > R13: 0000000000000000 R14: 0000000000001000 R15: 0000000000000ffb > > > FS: 00007fb29d8b2700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000 > > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > > CR2: ffff888021f7e005 CR3: 0000000026e7b000 CR4: 00000000003506f0 > > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > > Call Trace: > > > <TASK> > > > zero_user_segments include/linux/highmem.h:272 [inline] > > > folio_zero_range include/linux/highmem.h:428 [inline] > > > truncate_inode_partial_folio+0x76a/0xdf0 mm/truncate.c:237 > > > truncate_inode_pages_range+0x83b/0x1530 mm/truncate.c:381 > > > truncate_inode_pages mm/truncate.c:452 [inline] > > > truncate_pagecache+0x63/0x90 mm/truncate.c:753 > > > simple_setattr+0xed/0x110 fs/libfs.c:535 > > > secretmem_setattr+0xae/0xf0 mm/secretmem.c:170 > > > notify_change+0xb8c/0x12b0 fs/attr.c:424 > > > do_truncate+0x13c/0x200 fs/open.c:65 > > > do_sys_ftruncate+0x536/0x730 fs/open.c:193 > > > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > > > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 > > > entry_SYSCALL_64_after_hwframe+0x46/0xb0 > > > RIP: 0033:0x7fb29d900899 > > > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 > > > RSP: 002b:00007fb29d8b2318 EFLAGS: 00000246 ORIG_RAX: 000000000000004d > > > RAX: ffffffffffffffda RBX: 00007fb29d988408 RCX: 00007fb29d900899 > > > RDX: 00007fb29d900899 RSI: 0000000000000005 RDI: 0000000000000003 > > > RBP: 00007fb29d988400 R08: 0000000000000000 R09: 0000000000000000 > > > R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb29d98840c > > > R13: 00007ffca01a23bf R14: 00007fb29d8b2400 R15: 0000000000022000 > > > </TASK> > > > Modules linked in: > > > CR2: ffff888021f7e005 > > > ---[ end trace 0000000000000000 ]--- > > > > I think this is a bug in memfd_secret. secretmem_setattr() can race with a page > > being faulted in by secretmem_fault(). Specifically, a page can be faulted in > > after secretmem_setattr() has set i_size but before it zeroes out the partial > > page past i_size. memfd_secret pages aren't mapped in the kernel direct map, so > > the crash occurs when the kernel tries to zero out the partial page. > > > > I don't know what the best solution is -- maybe a rw_semaphore protecting > > secretmem_fault() and secretmem_setattr()? Or perhaps secretmem_setattr() > > should avoid the call to truncate_setsize() by not using simple_setattr(), given > > that secretmem_setattr() only supports the size going from zero to nonzero. > > From my perspective the rw_semaphore approach sounds reasonable. > > simple_setattr() and the functions it calls to do the actual work > isn't a tiny amount of code, it would be a shame to reimplement it in > secretmem.c. > > For the rwsem, I guess the idea is setattr will take it for write, and > fault will take it for read? Since setattr is a very infrequent > operation - a typical use case is you'd do it exactly once right after > opening the memfd_secret - this seems like it wouldn't make fault > significantly less performant. It's also a pretty small change I > think, just a few lines. Below is my take on adding a semaphore and making ->setattr() and ->fault() mutually exclusive. It's only lightly tested so I'd appreciate if Eric could give it a whirl. With addition of semaphore to secretmem_setattr() it seems we don't need special care for size changes, just calling simple_setattr() after taking the semaphore should be fine. Thoughts? >From edfcb2f0d31c2132bda483635dd2a8dd295efb04 Mon Sep 17 00:00:00 2001 From: Mike Rapoport <rppt@xxxxxxxxxxxxx> Date: Thu, 30 Jun 2022 11:26:37 +0300 Subject: [PATCH] secretmem: fix unhandled fault in truncate syzkaller reports the following issue: BUG: unable to handle page fault for address: ffff888021f7e005 PGD 11401067 P4D 11401067 PUD 11402067 PMD 21f7d063 PTE 800fffffde081060 Oops: 0002 [#1] PREEMPT SMP KASAN CPU: 0 PID: 3761 Comm: syz-executor281 Not tainted 5.19.0-rc4-syzkaller-00014-g941e3e791269 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:memset_erms+0x9/0x10 arch/x86/lib/memset_64.S:64 Code: c1 e9 03 40 0f b6 f6 48 b8 01 01 01 01 01 01 01 01 48 0f af c6 f3 48 ab 89 d1 f3 aa 4c 89 c8 c3 90 49 89 f9 40 88 f0 48 89 d1 <f3> aa 4c 89 c8 c3 90 49 89 fa 40 0f b6 ce 48 b8 01 01 01 01 01 01 RSP: 0018:ffffc9000329fa90 EFLAGS: 00010202 RAX: 0000000000000000 RBX: 0000000000001000 RCX: 0000000000000ffb RDX: 0000000000000ffb RSI: 0000000000000000 RDI: ffff888021f7e005 RBP: ffffea000087df80 R08: 0000000000000001 R09: ffff888021f7e005 R10: ffffed10043efdff R11: 0000000000000000 R12: 0000000000000005 R13: 0000000000000000 R14: 0000000000001000 R15: 0000000000000ffb FS: 00007fb29d8b2700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffff888021f7e005 CR3: 0000000026e7b000 CR4: 00000000003506f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> zero_user_segments include/linux/highmem.h:272 [inline] folio_zero_range include/linux/highmem.h:428 [inline] truncate_inode_partial_folio+0x76a/0xdf0 mm/truncate.c:237 truncate_inode_pages_range+0x83b/0x1530 mm/truncate.c:381 truncate_inode_pages mm/truncate.c:452 [inline] truncate_pagecache+0x63/0x90 mm/truncate.c:753 simple_setattr+0xed/0x110 fs/libfs.c:535 secretmem_setattr+0xae/0xf0 mm/secretmem.c:170 notify_change+0xb8c/0x12b0 fs/attr.c:424 do_truncate+0x13c/0x200 fs/open.c:65 do_sys_ftruncate+0x536/0x730 fs/open.c:193 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x46/0xb0 RIP: 0033:0x7fb29d900899 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fb29d8b2318 EFLAGS: 00000246 ORIG_RAX: 000000000000004d RAX: ffffffffffffffda RBX: 00007fb29d988408 RCX: 00007fb29d900899 RDX: 00007fb29d900899 RSI: 0000000000000005 RDI: 0000000000000003 RBP: 00007fb29d988400 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb29d98840c R13: 00007ffca01a23bf R14: 00007fb29d8b2400 R15: 0000000000022000 </TASK> Modules linked in: CR2: ffff888021f7e005 ---[ end trace 0000000000000000 ]--- Eric Biggers suggested that this happens when secretmem_setattr()->simple_setattr() races with secretmem_fault() so that a page that is faulted in by secretmem_fault() (and thus removed from the direct map) is zeroed by inode truncation right afterwards. Use an rw_semaphore to make secretmem_fault() and secretmem_setattr() mutually exclusive. Reported-by: syzbot+9bd2b7adbd34b30b87e4@xxxxxxxxxxxxxxxxxxxxxxxxx Suggested-by: Eric Biggers <ebiggers@xxxxxxxxxx> Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx> --- mm/secretmem.c | 48 ++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 40 insertions(+), 8 deletions(-) diff --git a/mm/secretmem.c b/mm/secretmem.c index 206ed6b40c1d..40573b045c96 100644 --- a/mm/secretmem.c +++ b/mm/secretmem.c @@ -47,30 +47,41 @@ bool secretmem_active(void) return !!atomic_read(&secretmem_users); } +struct secretmem_state { + struct rw_semaphore rw_sem; +}; + static vm_fault_t secretmem_fault(struct vm_fault *vmf) { struct address_space *mapping = vmf->vma->vm_file->f_mapping; struct inode *inode = file_inode(vmf->vma->vm_file); + struct secretmem_state *state = inode->i_private; pgoff_t offset = vmf->pgoff; gfp_t gfp = vmf->gfp_mask; unsigned long addr; struct page *page; + vm_fault_t ret; int err; if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode)) return vmf_error(-EINVAL); + down_read(&state->rw_sem); + retry: page = find_lock_page(mapping, offset); if (!page) { page = alloc_page(gfp | __GFP_ZERO); - if (!page) - return VM_FAULT_OOM; + if (!page) { + ret = VM_FAULT_OOM; + goto out; + } err = set_direct_map_invalid_noflush(page); if (err) { put_page(page); - return vmf_error(err); + ret = vmf_error(err); + goto out; } __SetPageUptodate(page); @@ -86,7 +97,8 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf) if (err == -EEXIST) goto retry; - return vmf_error(err); + ret = vmf_error(err); + goto out; } addr = (unsigned long)page_address(page); @@ -94,7 +106,11 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf) } vmf->page = page; - return VM_FAULT_LOCKED; + ret = VM_FAULT_LOCKED; + +out: + up_read(&state->rw_sem); + return ret; } static const struct vm_operations_struct secretmem_vm_ops = { @@ -163,11 +179,17 @@ static int secretmem_setattr(struct user_namespace *mnt_userns, { struct inode *inode = d_inode(dentry); unsigned int ia_valid = iattr->ia_valid; + struct secretmem_state *state = inode->i_private; + int ret; + down_write(&state->rw_sem); if ((ia_valid & ATTR_SIZE) && inode->i_size) - return -EINVAL; + ret = -EINVAL; + else + ret = simple_setattr(mnt_userns, dentry, iattr); + up_write(&state->rw_sem); - return simple_setattr(mnt_userns, dentry, iattr); + return ret; } static const struct inode_operations secretmem_iops = { @@ -179,22 +201,30 @@ static struct vfsmount *secretmem_mnt; static struct file *secretmem_file_create(unsigned long flags) { struct file *file = ERR_PTR(-ENOMEM); + struct secretmem_state *state; struct inode *inode; inode = alloc_anon_inode(secretmem_mnt->mnt_sb); if (IS_ERR(inode)) return ERR_CAST(inode); + state = kzalloc(sizeof(*state), GFP_KERNEL); + if (!state) + goto err_free_inode; + file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem", O_RDWR, &secretmem_fops); if (IS_ERR(file)) - goto err_free_inode; + goto err_free_state; mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER); mapping_set_unevictable(inode->i_mapping); + init_rwsem(&state->rw_sem); + inode->i_op = &secretmem_iops; inode->i_mapping->a_ops = &secretmem_aops; + inode->i_private = state; /* pretend we are a normal file with zero size */ inode->i_mode |= S_IFREG; @@ -202,6 +232,8 @@ static struct file *secretmem_file_create(unsigned long flags) return file; +err_free_state: + kfree(state); err_free_inode: iput(inode); return file; base-commit: 03c765b0e3b4cb5063276b086c76f7a612856a9a -- 2.34.1 > > The following commit tried to fix a similar bug, but it wasn't enough: > > > > commit f9b141f93659e09a52e28791ccbaf69c273b8e92 > > Author: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> > > Date: Thu Apr 14 19:13:31 2022 -0700 > > > > mm/secretmem: fix panic when growing a memfd_secret > > > > > > Here's a simplified reproducer. Note, for memfd_secret to be supported, the > > kernel config must contain CONFIG_SECRETMEM=y and the kernel command line must > > contain secretmem.enable=1. > > > > #include <pthread.h> > > #include <setjmp.h> > > #include <signal.h> > > #include <sys/mman.h> > > #include <sys/syscall.h> > > #include <unistd.h> > > > > static volatile int fd; > > static jmp_buf jump_buf; > > > > static void *truncate_thread(void *arg) > > { > > for (;;) > > ftruncate(fd, 1000); > > } > > > > static void handle_sigbus(int sig) > > { > > longjmp(jump_buf, 1); > > } > > > > int main(void) > > { > > struct sigaction act = { > > .sa_handler = handle_sigbus, > > .sa_flags = SA_NODEFER, > > }; > > pthread_t t; > > void *addr; > > > > sigaction(SIGBUS, &act, NULL); > > > > pthread_create(&t, NULL, truncate_thread, NULL); > > for (;;) { > > fd = syscall(__NR_memfd_secret, 0); > > addr = mmap(NULL, 8192, PROT_WRITE, MAP_SHARED, fd, 0); > > if (setjmp(jump_buf) == 0) > > *(unsigned int *)addr = 0; > > munmap(addr, 8192); > > close(fd); > > } > > } -- Sincerely yours, Mike.
