{"id":"DEBIAN-CVE-2021-47531","details":"In the Linux kernel, the following vulnerability has been resolved:  drm/msm: Fix mmap to include VM_IO and VM_DONTDUMP  In commit 510410bfc034 (\"drm/msm: Implement mmap as GEM object function\") we switched to a new/cleaner method of doing things. That's good, but we missed a little bit.  Before that commit, we used to _first_ run through the drm_gem_mmap_obj() case where `obj-\u003efuncs-\u003emmap()` was NULL. That meant that we ran:    vma-\u003evm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;   vma-\u003evm_page_prot = pgprot_writecombine(vm_get_page_prot(vma-\u003evm_flags));   vma-\u003evm_page_prot = pgprot_decrypted(vma-\u003evm_page_prot);  ...and _then_ we modified those mappings with our own. Now that `obj-\u003efuncs-\u003emmap()` is no longer NULL we don't run the default code. It looks like the fact that the vm_flags got VM_IO / VM_DONTDUMP was important because we're now getting crashes on Chromebooks that use ARC++ while logging out. Specifically a crash that looks like this (this is on a 5.10 kernel w/ relevant backports but also seen on a 5.15 kernel):    Unable to handle kernel paging request at virtual address ffffffc008000000   Mem abort info:     ESR = 0x96000006     EC = 0x25: DABT (current EL), IL = 32 bits     SET = 0, FnV = 0     EA = 0, S1PTW = 0   Data abort info:     ISV = 0, ISS = 0x00000006     CM = 0, WnR = 0   swapper pgtable: 4k pages, 39-bit VAs, pgdp=000000008293d000   [ffffffc008000000] pgd=00000001002b3003, p4d=00000001002b3003,                      pud=00000001002b3003, pmd=0000000000000000   Internal error: Oops: 96000006 [#1] PREEMPT SMP   [...]   CPU: 7 PID: 15734 Comm: crash_dump64 Tainted: G W 5.10.67 #1 [...]   Hardware name: Qualcomm Technologies, Inc. sc7280 IDP SKU2 platform (DT)   pstate: 80400009 (Nzcv daif +PAN -UAO -TCO BTYPE=--)   pc : __arch_copy_to_user+0xc0/0x30c   lr : copyout+0xac/0x14c   [...]   Call trace:    __arch_copy_to_user+0xc0/0x30c    copy_page_to_iter+0x1a0/0x294    process_vm_rw_core+0x240/0x408    process_vm_rw+0x110/0x16c    __arm64_sys_process_vm_readv+0x30/0x3c    el0_svc_common+0xf8/0x250    do_el0_svc+0x30/0x80    el0_svc+0x10/0x1c    el0_sync_handler+0x78/0x108    el0_sync+0x184/0x1c0   Code: f8408423 f80008c3 910020c6 36100082 (b8404423)  Let's add the two flags back in.  While we're at it, the fact that we aren't running the default means that we _don't_ need to clear out VM_PFNMAP, so remove that and save an instruction.  NOTE: it was confirmed that VM_IO was the important flag to fix the problem I was seeing, but adding back VM_DONTDUMP seems like a sane thing to do so I'm doing that too.","modified":"2026-09-01T20:04:38.015900503Z","published":"2024-05-24T15:15:16.357Z","upstream":["CVE-2021-47531"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2021-47531"}],"affected":[{"package":{"name":"linux","ecosystem":"Debian:12","purl":"pkg:deb/debian/linux?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.15.15-1"}]}],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2021-47531.json"}},{"package":{"name":"linux","ecosystem":"Debian:13","purl":"pkg:deb/debian/linux?arch=source&distro=trixie"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.15.15-1"}]}],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2021-47531.json"}},{"package":{"name":"linux","ecosystem":"Debian:14","purl":"pkg:deb/debian/linux?arch=source&distro=forky"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.15.15-1"}]}],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2021-47531.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"}]}