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rseq: Fix rseq registration with CONFIG_DEBUG_RSEQ

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With CONFIG_DEBUG_RSEQ=y, at rseq registration the read-only fields are
copied from user-space, if this copy fails the syscall returns -EFAULT
and the registration should not be activated - but it erroneously is.

Move the activation of the registration after the copy of the fields to
fix this bug.

Fixes: 7d5265ffcd ("rseq: Validate read-only fields under DEBUG_RSEQ config")
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/r/20250219205330.324770-1-mjeanson@efficios.com
This commit is contained in:
Michael Jeanson 2025-02-19 15:53:26 -05:00 • committed by Ingo Molnar
parent 02d954c0fd
commit dc0a241cea
1 changed files with 8 additions and 3 deletions
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11
kernel/rseq.c
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@ -507,9 +507,6 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len,
return -EINVAL;
if (!access_ok(rseq, rseq_len))
return -EFAULT;
current->rseq = rseq;
current->rseq_len = rseq_len;
current->rseq_sig = sig;
#ifdef CONFIG_DEBUG_RSEQ
/*
* Initialize the in-kernel rseq fields copy for validation of
@ -521,6 +518,14 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len,
get_user(rseq_kernel_fields(current)->mm_cid, &rseq->mm_cid))
return -EFAULT;
#endif
/*
* Activate the registration by setting the rseq area address, length
* and signature in the task struct.
*/
current->rseq = rseq;
current->rseq_len = rseq_len;
current->rseq_sig = sig;
/*
* If rseq was previously inactive, and has just been
* registered, ensure the cpu_id_start and cpu_id fields