CVE-2021-47303 SUSE CVE security@suse.de SUSE Security Team SUSE CVE-2021-47303 Interim 1 9 2025-05-13T00:17:37Z current 2024-05-22T23:39:54Z 2025-05-13T00:17:37Z cve-database/bin/generate-cvrf-cve.pl 2020-12-27T01:00:00Z CVE-2021-47303 In the Linux kernel, the following vulnerability has been resolved: bpf: Track subprog poke descriptors correctly and fix use-after-free Subprograms are calling map_poke_track(), but on program release there is no hook to call map_poke_untrack(). However, on program release, the aux memory (and poke descriptor table) is freed even though we still have a reference to it in the element list of the map aux data. When we run map_poke_run(), we then end up accessing free'd memory, triggering KASAN in prog_array_map_poke_run(): [...] [ 402.824689] BUG: KASAN: use-after-free in prog_array_map_poke_run+0xc2/0x34e [ 402.824698] Read of size 4 at addr ffff8881905a7940 by task hubble-fgs/4337 [ 402.824705] CPU: 1 PID: 4337 Comm: hubble-fgs Tainted: G I 5.12.0+ #399 [ 402.824715] Call Trace: [ 402.824719] dump_stack+0x93/0xc2 [ 402.824727] print_address_description.constprop.0+0x1a/0x140 [ 402.824736] ? prog_array_map_poke_run+0xc2/0x34e [ 402.824740] ? prog_array_map_poke_run+0xc2/0x34e [ 402.824744] kasan_report.cold+0x7c/0xd8 [ 402.824752] ? prog_array_map_poke_run+0xc2/0x34e [ 402.824757] prog_array_map_poke_run+0xc2/0x34e [ 402.824765] bpf_fd_array_map_update_elem+0x124/0x1a0 [...] The elements concerned are walked as follows: for (i = 0; i < elem->aux->size_poke_tab; i++) { poke = &elem->aux->poke_tab[i]; [...] The access to size_poke_tab is a 4 byte read, verified by checking offsets in the KASAN dump: [ 402.825004] The buggy address belongs to the object at ffff8881905a7800 which belongs to the cache kmalloc-1k of size 1024 [ 402.825008] The buggy address is located 320 bytes inside of 1024-byte region [ffff8881905a7800, ffff8881905a7c00) The pahole output of bpf_prog_aux: struct bpf_prog_aux { [...] /* --- cacheline 5 boundary (320 bytes) --- */ u32 size_poke_tab; /* 320 4 */ [...] In general, subprograms do not necessarily manage their own data structures. For example, BTF func_info and linfo are just pointers to the main program structure. This allows reference counting and cleanup to be done on the latter which simplifies their management a bit. The aux->poke_tab struct, however, did not follow this logic. The initial proposed fix for this use-after-free bug further embedded poke data tracking into the subprogram with proper reference counting. However, Daniel and Alexei questioned why we were treating these objects special; I agree, its unnecessary. The fix here removes the per subprogram poke table allocation and map tracking and instead simply points the aux->poke_tab pointer at the main programs poke table. This way, map tracking is simplified to the main program and we do not need to manage them per subprogram. This also means, bpf_prog_free_deferred(), which unwinds the program reference counting and kfrees objects, needs to ensure that we don't try to double free the poke_tab when free'ing the subprog structures. This is easily solved by NULL'ing the poke_tab pointer. The second detail is to ensure that per subprogram JIT logic only does fixups on poke_tab[] entries it owns. To do this, we add a pointer in the poke structure to point at the subprogram value so JITs can easily check while walking the poke_tab structure if the current entry belongs to the current program. The aux pointer is stable and therefore suitable for such comparison. On the jit_subprogs() error path, we omit cleaning up the poke->aux field because these are only ever referenced from the JIT side, but on error we will never make it to the JIT, so its fine to leave them dangling. Removing these pointers would complicate the error path for no reason. However, we do need to untrack all poke descriptors from the main program as otherwise they could race with the freeing of JIT memory from the subprograms. Lastly, a748c6975dea3 ("bpf: propagate poke des ---truncated--- The CVRF data is provided by SUSE under the Creative Commons License 4.0 with Attribution (CC-BY-4.0). https://www.suse.com/support/security/rating/ SUSE Security Ratings SUSE Enterprise Storage 7.1 SUSE Linux Enterprise Module for Basesystem 15 SP5 SUSE Linux Enterprise Module for Development Tools 15 SP5 SUSE Linux Enterprise Module for Basesystem 15 SP6 SUSE Linux Enterprise Module for Development Tools 15 SP6 SUSE Linux Enterprise High Performance Computing 12 SP5 SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS SUSE Linux Enterprise Module for Basesystem 15 SP5 SUSE Linux Enterprise Module for Development Tools 15 SP5 SUSE Linux Enterprise Module for Public Cloud 15 SP5 SUSE Linux Enterprise Module for Basesystem 15 SP6 SUSE 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Leap 15.5 dlm-kmp-default as a component of openSUSE Leap 15.5 gfs2-kmp-default as a component of openSUSE Leap 15.5 kernel-default as a component of openSUSE Leap 15.5 kernel-default-devel as a component of openSUSE Leap 15.5 kernel-default-extra as a component of openSUSE Leap 15.5 kernel-default-livepatch as a component of openSUSE Leap 15.5 kernel-default-livepatch-devel as a component of openSUSE Leap 15.5 kernel-default-optional as a component of openSUSE Leap 15.5 kernel-default-vdso as a component of openSUSE Leap 15.5 kselftests-kmp-default as a component of openSUSE Leap 15.5 ocfs2-kmp-default as a component of openSUSE Leap 15.5 reiserfs-kmp-default as a component of openSUSE Leap 15.5 kernel-devel as a component of openSUSE Leap 15.5 kernel-macros as a component of openSUSE Leap 15.5 kernel-source as a component of openSUSE Leap 15.5 kernel-source-vanilla as a component of openSUSE Leap 15.5 kernel-devel-azure as a component of openSUSE Leap 15.5 kernel-source-azure as a component of openSUSE Leap 15.5 kernel-devel-rt as a component of openSUSE Leap 15.5 kernel-source-rt as a component of openSUSE Leap 15.5 cluster-md-kmp-default as a component of openSUSE Leap 15.6 dlm-kmp-default as a component of openSUSE Leap 15.6 gfs2-kmp-default as a component of openSUSE Leap 15.6 kernel-default as a component of openSUSE Leap 15.6 kernel-default-devel as a component of openSUSE Leap 15.6 kernel-default-extra as a component of openSUSE Leap 15.6 kernel-default-livepatch as a component of openSUSE Leap 15.6 kernel-default-livepatch-devel as a component of openSUSE Leap 15.6 kernel-default-optional as a component of openSUSE Leap 15.6 kernel-default-vdso as a component of openSUSE Leap 15.6 kselftests-kmp-default as a component of openSUSE Leap 15.6 ocfs2-kmp-default as a component of openSUSE Leap 15.6 reiserfs-kmp-default as a component of openSUSE Leap 15.6 kernel-devel as a component of openSUSE Leap 15.6 kernel-macros as a component of openSUSE Leap 15.6 kernel-source as a component of openSUSE Leap 15.6 kernel-source-vanilla as a component of openSUSE Leap 15.6 kernel-devel-azure as a component of openSUSE Leap 15.6 kernel-source-azure as a component of openSUSE Leap 15.6 kernel-devel-rt as a component of openSUSE Leap 15.6 kernel-source-rt as a component of openSUSE Leap 15.6 In the Linux kernel, the following vulnerability has been resolved: bpf: Track subprog poke descriptors correctly and fix use-after-free Subprograms are calling map_poke_track(), but on program release there is no hook to call map_poke_untrack(). However, on program release, the aux memory (and poke descriptor table) is freed even though we still have a reference to it in the element list of the map aux data. When we run map_poke_run(), we then end up accessing free'd memory, triggering KASAN in prog_array_map_poke_run(): [...] [ 402.824689] BUG: KASAN: use-after-free in prog_array_map_poke_run+0xc2/0x34e [ 402.824698] Read of size 4 at addr ffff8881905a7940 by task hubble-fgs/4337 [ 402.824705] CPU: 1 PID: 4337 Comm: hubble-fgs Tainted: G I 5.12.0+ #399 [ 402.824715] Call Trace: [ 402.824719] dump_stack+0x93/0xc2 [ 402.824727] print_address_description.constprop.0+0x1a/0x140 [ 402.824736] ? prog_array_map_poke_run+0xc2/0x34e [ 402.824740] ? prog_array_map_poke_run+0xc2/0x34e [ 402.824744] kasan_report.cold+0x7c/0xd8 [ 402.824752] ? prog_array_map_poke_run+0xc2/0x34e [ 402.824757] prog_array_map_poke_run+0xc2/0x34e [ 402.824765] bpf_fd_array_map_update_elem+0x124/0x1a0 [...] The elements concerned are walked as follows: for (i = 0; i < elem->aux->size_poke_tab; i++) { poke = &elem->aux->poke_tab[i]; [...] The access to size_poke_tab is a 4 byte read, verified by checking offsets in the KASAN dump: [ 402.825004] The buggy address belongs to the object at ffff8881905a7800 which belongs to the cache kmalloc-1k of size 1024 [ 402.825008] The buggy address is located 320 bytes inside of 1024-byte region [ffff8881905a7800, ffff8881905a7c00) The pahole output of bpf_prog_aux: struct bpf_prog_aux { [...] /* --- cacheline 5 boundary (320 bytes) --- */ u32 size_poke_tab; /* 320 4 */ [...] In general, subprograms do not necessarily manage their own data structures. For example, BTF func_info and linfo are just pointers to the main program structure. This allows reference counting and cleanup to be done on the latter which simplifies their management a bit. The aux->poke_tab struct, however, did not follow this logic. The initial proposed fix for this use-after-free bug further embedded poke data tracking into the subprogram with proper reference counting. However, Daniel and Alexei questioned why we were treating these objects special; I agree, its unnecessary. The fix here removes the per subprogram poke table allocation and map tracking and instead simply points the aux->poke_tab pointer at the main programs poke table. This way, map tracking is simplified to the main program and we do not need to manage them per subprogram. This also means, bpf_prog_free_deferred(), which unwinds the program reference counting and kfrees objects, needs to ensure that we don't try to double free the poke_tab when free'ing the subprog structures. This is easily solved by NULL'ing the poke_tab pointer. The second detail is to ensure that per subprogram JIT logic only does fixups on poke_tab[] entries it owns. To do this, we add a pointer in the poke structure to point at the subprogram value so JITs can easily check while walking the poke_tab structure if the current entry belongs to the current program. The aux pointer is stable and therefore suitable for such comparison. On the jit_subprogs() error path, we omit cleaning up the poke->aux field because these are only ever referenced from the JIT side, but on error we will never make it to the JIT, so its fine to leave them dangling. Removing these pointers would complicate the error path for no reason. However, we do need to untrack all poke descriptors from the main program as otherwise they could race with the freeing of JIT memory from the subprograms. Lastly, a748c6975dea3 ("bpf: propagate poke des ---truncated--- CVE-2021-47303 SUSE Enterprise Storage 7.1:kernel-default SUSE Enterprise Storage 7.1:kernel-default-devel SUSE Enterprise Storage 7.1:kernel-devel SUSE Enterprise Storage 7.1:kernel-macros SUSE Enterprise Storage 7.1:kernel-source SUSE Enterprise Storage 7.1:reiserfs-kmp-default SUSE Linux Enterprise High Performance Computing 12 SP5:kernel-default SUSE Linux Enterprise High Performance Computing 12 SP5:kernel-source SUSE Linux Enterprise High Performance Computing 12 SP5:kernel-source-azure SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS:kernel-default SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS:kernel-default-devel SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS:kernel-devel SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS:kernel-macros SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS:kernel-source SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS:kernel-default SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS:kernel-default-devel SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS:kernel-devel SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS:kernel-macros SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS:kernel-source SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS:reiserfs-kmp-default SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS:kernel-default SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS:kernel-default-devel SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS:kernel-devel SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS:kernel-macros SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS:kernel-source SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS:reiserfs-kmp-default SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS:kernel-default SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS:kernel-default-devel SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS:kernel-devel SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS:kernel-macros SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS:kernel-source SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS:reiserfs-kmp-default SUSE Linux Enterprise Micro 5.0:kernel-default SUSE Linux Enterprise Micro 5.1:kernel-default SUSE Linux Enterprise Micro 5.1:kernel-rt SUSE Linux Enterprise Micro 5.1:kernel-source-rt SUSE Linux Enterprise Micro 5.2:kernel-default SUSE Linux Enterprise Micro 5.2:kernel-rt SUSE Linux Enterprise Micro 5.2:kernel-source-rt SUSE Linux Enterprise Micro 5.3:kernel-default SUSE Linux Enterprise Micro 5.3:kernel-rt SUSE Linux Enterprise Micro 5.3:kernel-source-rt SUSE Linux Enterprise Micro 5.4:kernel-default SUSE Linux Enterprise Micro 5.4:kernel-rt SUSE Linux Enterprise Micro 5.4:kernel-source-rt SUSE Linux Enterprise Micro 5.5:kernel-devel-rt SUSE 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