Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider:
New issues: - [High] The strict `size != sizeof(data)` check completely breaks UAPI backward and forward compatibility for extensible structs. - [Medium] Silent truncation of the 64-bit `eh_frame_hdr_start` address to a 32-bit `unsigned long` during unregistration on 32-bit architectures. Pre-existing issues: - [High] If `mas_erase` fails due to an out-of-memory condition, it returns the target entry but leaves it in the maple tree. `__eh_frame_remove_section` fails to check `mas_is_err(mas)`, freeing the entry while it remains accessible in the tree. - [High] The unregister prctl triggers an unbounded iteration over the maple tree while holding a spinlock, allowing an unprivileged user to cause a CPU soft lockup. -- --- Patch [24]: [RFC PATCH v2 24/24] unwind_user/eh_frame: Add prctl() interface for (un)registering .eh_frame_hdr sections --- commit 51adfd3b1e2795e1bc35c760119a8842b4e76983 Author: Jens Remus <[email protected]> unwind_user/eh_frame: Add prctl() interface for (un)registering .eh_frame_hdr sections This commit adds prctl interfaces to register and unregister .eh_frame_hdr sections. It allows dynamic linkers to notify the kernel about the location of these sections using a new eh_frame_setup structure. Link: https://lore.kernel.org/all/[email protected]/ > diff --git a/kernel/unwind/eh_frame.c b/kernel/unwind/eh_frame.c > --- a/kernel/unwind/eh_frame.c > +++ b/kernel/unwind/eh_frame.c [ ... ] > @@ -1609,3 +1610,48 @@ void eh_frame_free_mm(struct mm_struct *mm) > > mtree_destroy(&mm->eh_frame_mt); > } > + > +int eh_frame_register(struct eh_frame_setup __user *user_data, > __kernel_size_t size) > +{ > + struct eh_frame_setup data; > + unsigned long eh_frame_hdr_end, text_end; > + > + if (!user_data || !size) > + return -EINVAL; > + > + if (size != sizeof(data)) > + return -EINVAL; [Severity: High] Does this strict size check prevent future UAPI extensions? Since this is a new UAPI structure, rejecting sizes that do not exactly match the kernel's structure size prevents extending the structure later without breaking backward compatibility. Would it be better to use copy_struct_from_user() here to handle size mismatches by verifying trailing zeroes? > + > + if (copy_from_user(&data, user_data, sizeof(data))) > + return -EFAULT; > + > + if (check_add_overflow(data.eh_frame_hdr_start, data.eh_frame_hdr_size, > + &eh_frame_hdr_end)) > + return -EINVAL; > + > + if (check_add_overflow(data.text_start, data.text_size, &text_end)) > + return -EINVAL; > + > + return eh_frame_add_section(data.eh_frame_hdr_start, eh_frame_hdr_end, > + data.text_start, text_end); > +} > + > +int eh_frame_unregister(struct eh_frame_setup __user *user_data, > __kernel_size_t size) > +{ > + struct eh_frame_setup data; > + > + if (!user_data || !size) > + return -EINVAL; > + > + if (size != sizeof(data)) > + return -EINVAL; [Severity: High] Is this strict size check similarly going to cause extensibility issues for the unregister path? Like the register function, could this use copy_struct_from_user() to safely allow future modifications? > + > + if (copy_from_user(&data, user_data, sizeof(data))) > + return -EFAULT; > + > + /* Unregister only uses eh_frame_hdr_start */ > + if (data.eh_frame_hdr_size || data.text_start || data.text_size) > + return -EINVAL; > + > + return eh_frame_remove_section(data.eh_frame_hdr_start); [Severity: Medium] Will data.eh_frame_hdr_start be silently truncated on 32-bit architectures? The user provides a 64-bit __u64 address, but eh_frame_remove_section() expects an unsigned long. If the upper 32 bits are set by userspace on a 32-bit architecture, this could truncate into a valid 32-bit address without any bounds validation. [Severity: High] This isn't a bug introduced by this patch, but does exposing this function to userspace via prctl allow an unprivileged user to cause a CPU soft lockup? Looking at eh_frame_remove_section(), it performs an unbounded iteration over the maple tree while holding a spinlock: kernel/unwind/eh_frame.c:eh_frame_remove_section() { ... mtree_lock(&mm->eh_frame_mt); mas_for_each(&mas, sec, ULONG_MAX) { if (sec->eh_frame_hdr_start == eh_frame_hdr_start) { found = true; ret |= __eh_frame_remove_section(&mas, sec); } } mtree_unlock(&mm->eh_frame_mt); ... } Could an attacker register a massive number of non-overlapping sections and then trigger a long unbounded loop with preemption disabled? [Severity: High] This is also a pre-existing issue, but the new prctl makes it trivially reachable by unprivileged userspace, which could lead to a use-after-free. When __eh_frame_remove_section() attempts to remove a section: kernel/unwind/eh_frame.c:__eh_frame_remove_section() { ... if (mas_erase(mas) != sec) { dbg_sec("mas_erase failed: text=%lx\n", sec->text_start); return -EINVAL; } call_srcu(&eh_frame_srcu, &sec->rcu, eh_frame_free_srcu); ... } If mas_erase() fails due to an out-of-memory condition, it can set an error state and return the target entry without removing it from the tree. Because the code does not check mas_is_err(mas), it frees the entry while it remains accessible in the maple tree. Should this verify mas_is_err() before freeing the section? > +} -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=24
