cve-2023-52452
Vulnerability from cvelistv5
Published
2024-02-22 16:21
Modified
2024-12-19 08:19
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: bpf: Fix accesses to uninit stack slots Privileged programs are supposed to be able to read uninitialized stack memory (ever since 6715df8d5) but, before this patch, these accesses were permitted inconsistently. In particular, accesses were permitted above state->allocated_stack, but not below it. In other words, if the stack was already "large enough", the access was permitted, but otherwise the access was rejected instead of being allowed to "grow the stack". This undesired rejection was happening in two places: - in check_stack_slot_within_bounds() - in check_stack_range_initialized() This patch arranges for these accesses to be permitted. A bunch of tests that were relying on the old rejection had to change; all of them were changed to add also run unprivileged, in which case the old behavior persists. One tests couldn't be updated - global_func16 - because it can't run unprivileged for other reasons. This patch also fixes the tracking of the stack size for variable-offset reads. This second fix is bundled in the same commit as the first one because they're inter-related. Before this patch, writes to the stack using registers containing a variable offset (as opposed to registers with fixed, known values) were not properly contributing to the function's needed stack size. As a result, it was possible for a program to verify, but then to attempt to read out-of-bounds data at runtime because a too small stack had been allocated for it. Each function tracks the size of the stack it needs in bpf_subprog_info.stack_depth, which is maintained by update_stack_depth(). For regular memory accesses, check_mem_access() was calling update_state_depth() but it was passing in only the fixed part of the offset register, ignoring the variable offset. This was incorrect; the minimum possible value of that register should be used instead. This tracking is now fixed by centralizing the tracking of stack size in grow_stack_state(), and by lifting the calls to grow_stack_state() to check_stack_access_within_bounds() as suggested by Andrii. The code is now simpler and more convincingly tracks the correct maximum stack size. check_stack_range_initialized() can now rely on enough stack having been allocated for the access; this helps with the fix for the first issue. A few tests were changed to also check the stack depth computation. The one that fails without this patch is verifier_var_off:stack_write_priv_vs_unpriv.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/0954982db8283016bf38e9db2da5adf47a102e19Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/6b4a64bafd107e521c01eec3453ce94a3fb38529Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/fbcf372c8eda2290470268e0afb5ab5d5f5d5fdePatch
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/0954982db8283016bf38e9db2da5adf47a102e19Patch
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/6b4a64bafd107e521c01eec3453ce94a3fb38529Patch
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/fbcf372c8eda2290470268e0afb5ab5d5f5d5fdePatch
Impacted products
Vendor Product Version
Linux Linux Version: 5.12
Show details on NVD website

To clipboard 

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Antes de este parche, las escrituras en la pila usando registros que conten\u00edan un desplazamiento variable (a diferencia de registros con valores fijos y conocidos) no contribu\u00edan adecuadamente al tama\u00f1o de pila necesario de la funci\u00f3n. Como resultado, era posible que un programa verificara, pero luego intentara leer datos fuera de l\u00edmites en tiempo de ejecuci\u00f3n porque se le hab\u00eda asignado una pila demasiado peque\u00f1a. Cada funci\u00f3n rastrea el tama\u00f1o de la pila que necesita en bpf_subprog_info.stack_ Depth, que es mantenido por update_stack_ Depth(). Para accesos regulares a la memoria, check_mem_access() estaba llamando a update_state_ Depth() pero pasaba solo la parte fija del registro de compensaci\u00f3n, ignorando la variable compensaci\u00f3n. Esto era incorrecto; en su lugar se debe utilizar el valor m\u00ednimo posible de ese registro. 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}


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