CVE-2024-50164 (GCVE-0-2024-50164)
Vulnerability from cvelistv5
Published
2024-11-07 09:31
Modified
2025-11-03 20:43
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: bpf: Fix overloading of MEM_UNINIT's meaning Lonial reported an issue in the BPF verifier where check_mem_size_reg() has the following code: if (!tnum_is_const(reg->var_off)) /* For unprivileged variable accesses, disable raw * mode so that the program is required to * initialize all the memory that the helper could * just partially fill up. */ meta = NULL; This means that writes are not checked when the register containing the size of the passed buffer has not a fixed size. Through this bug, a BPF program can write to a map which is marked as read-only, for example, .rodata global maps. The problem is that MEM_UNINIT's initial meaning that "the passed buffer to the BPF helper does not need to be initialized" which was added back in commit 435faee1aae9 ("bpf, verifier: add ARG_PTR_TO_RAW_STACK type") got overloaded over time with "the passed buffer is being written to". The problem however is that checks such as the above which were added later via 06c1c049721a ("bpf: allow helpers access to variable memory") set meta to NULL in order force the user to always initialize the passed buffer to the helper. Due to the current double meaning of MEM_UNINIT, this bypasses verifier write checks to the memory (not boundary checks though) and only assumes the latter memory is read instead. Fix this by reverting MEM_UNINIT back to its original meaning, and having MEM_WRITE as an annotation to BPF helpers in order to then trigger the BPF verifier checks for writing to memory. Some notes: check_arg_pair_ok() ensures that for ARG_CONST_SIZE{,_OR_ZERO} we can access fn->arg_type[arg - 1] since it must contain a preceding ARG_PTR_TO_MEM. For check_mem_reg() the meta argument can be removed altogether since we do check both BPF_READ and BPF_WRITE. Same for the equivalent check_kfunc_mem_size_reg().
References
Impacted products
Vendor Product Version
Linux Linux Version: 97e6d7dab1ca4648821c790a2b7913d6d5d549db
Version: 97e6d7dab1ca4648821c790a2b7913d6d5d549db
Version: 97e6d7dab1ca4648821c790a2b7913d6d5d549db
Version: 97e6d7dab1ca4648821c790a2b7913d6d5d549db
Version: 6099a6c8a749a5c8d5f8b4c4342022a92072a02b
Version: bfe25df63048edd4ceaf78a2fc755d5e2befc978
Version: 717c39718dbc4f7ebcbb7b625fb11851cd9007fe
Version: 5d0bba8232bf22ce13747cbfc8f696318ff01a50
Version: 70674d11d14eeecad90be4b409a22b902112ba32
Version: a08d942ecbf46e23a192093f6983cb1d779f4fa8
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix overloading of MEM_UNINIT\u0027s meaning\n\nLonial reported an issue in the BPF verifier where check_mem_size_reg()\nhas the following code:\n\n    if (!tnum_is_const(reg-\u003evar_off))\n        /* For unprivileged variable accesses, disable raw\n         * mode so that the program is required to\n         * initialize all the memory that the helper could\n         * just partially fill up.\n         */\n         meta = NULL;\n\nThis means that writes are not checked when the register containing the\nsize of the passed buffer has not a fixed size. Through this bug, a BPF\nprogram can write to a map which is marked as read-only, for example,\n.rodata global maps.\n\nThe problem is that MEM_UNINIT\u0027s initial meaning that \"the passed buffer\nto the BPF helper does not need to be initialized\" which was added back\nin commit 435faee1aae9 (\"bpf, verifier: add ARG_PTR_TO_RAW_STACK type\")\ngot overloaded over time with \"the passed buffer is being written to\".\n\nThe problem however is that checks such as the above which were added later\nvia 06c1c049721a (\"bpf: allow helpers access to variable memory\") set meta\nto NULL in order force the user to always initialize the passed buffer to\nthe helper. Due to the current double meaning of MEM_UNINIT, this bypasses\nverifier write checks to the memory (not boundary checks though) and only\nassumes the latter memory is read instead.\n\nFix this by reverting MEM_UNINIT back to its original meaning, and having\nMEM_WRITE as an annotation to BPF helpers in order to then trigger the\nBPF verifier checks for writing to memory.\n\nSome notes: check_arg_pair_ok() ensures that for ARG_CONST_SIZE{,_OR_ZERO}\nwe can access fn-\u003earg_type[arg - 1] since it must contain a preceding\nARG_PTR_TO_MEM. For check_mem_reg() the meta argument can be removed\naltogether since we do check both BPF_READ and BPF_WRITE. Same for the\nequivalent check_kfunc_mem_size_reg()."
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    "dateUpdated": "2025-11-03T20:43:57.432Z",
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