CVE-2021-47492

In the Linux kernel, the following vulnerability has been resolved:

mm, thp: bail out early in collapse_file for writeback page

Currently collapsefile does not explicitly check PGwriteback, instead, pagehasprivate and trytorelease_page are used to filter writeback pages. This does not work for xfs with blocksize equal to or larger than pagesize, because in such case xfs has no page->private.

This makes collapsefile bail out early for writeback page. Otherwise, xfs endpage_writeback will panic as follows.

page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:ffff0003f88c86a8 index:0x0 pfn:0x84ef32 aops:xfsaddressspaceoperations [xfs] ino:30000b7 dentry name:"libtest.so" flags: 0x57fffe0000008027(locked|referenced|uptodate|active|writeback) raw: 57fffe0000008027 ffff80001b48bc28 ffff80001b48bc28 ffff0003f88c86a8 raw: 0000000000000000 0000000000000000 00000000ffffffff ffff0000c3e9a000 page dumped because: VMBUGONPAGE(((unsigned int) pagerefcount(page) + 127u <= 127u)) page->memcgroup:ffff0000c3e9a000 ------------[ cut here ]------------ kernel BUG at include/linux/mm.h:1212! Internal error: Oops - BUG: 0 [#1] SMP Modules linked in: BUG: Bad page state in process khugepaged pfn:84ef32 xfs(E) page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:0 index:0x0 pfn:0x84ef32 libcrc32c(E) rfkill(E) aesceblk(E) cryptosimd(E) ... CPU: 25 PID: 0 Comm: swapper/25 Kdump: loaded Tainted: ... pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--) Call trace: endpagewriteback+0x1c0/0x214 iomapfinishpagewriteback+0x13c/0x204 iomapfinishioend+0xe8/0x19c iomapwritepageendbio+0x38/0x50 bioendio+0x168/0x1ec blkupdaterequest+0x278/0x3f0 blkmqendrequest+0x34/0x15c virtblkrequestdone+0x38/0x74 [virtioblk] blkdonesoftirq+0xc4/0x110 _dosoftirq+0x128/0x38c _irqexitrcu+0x118/0x150 irqexit+0x1c/0x30 _handledomainirq+0x8c/0xf0 gichandleirq+0x84/0x108 el1irq+0xcc/0x180 archcpuidle+0x18/0x40 defaultidlecall+0x4c/0x1a0 cpuidleidlecall+0x168/0x1e0 doidle+0xb4/0x104 cpustartupentry+0x30/0x9c secondarystartkernel+0x104/0x180 Code: d4210000 b0006161 910c8021 94013f4d (d4210000) ---[ end trace 4a88c6a074082f8c ]--- Kernel panic - not syncing: Oops - BUG: Fatal exception in interrupt