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fix for the breakage spotted by Neil in the interplay between /proc/sys

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->d_compare() weirdness and parallel lookups
 
 Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Merge tag 'pull-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull /proc/sys dcache lookup fix from Al Viro:
 "Fix for the breakage spotted by Neil in the interplay between
  /proc/sys ->d_compare() weirdness and parallel lookups"

* tag 'pull-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  fix proc_sys_compare() handling of in-lookup dentries
This commit is contained in:
Linus Torvalds 2025-07-06 13:10:39 -07:00
commit bab5cac627
2 changed files with 12 additions and 8 deletions
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2
fs/proc/inode.c
View File

@ -42,7 +42,7 @@ static void proc_evict_inode(struct inode *inode)
head = ei->sysctl;
if (head) {
RCU_INIT_POINTER(ei->sysctl, NULL);
WRITE_ONCE(ei->sysctl, NULL);
proc_sys_evict_inode(inode, head);
}
}

18
fs/proc/proc_sysctl.c
View File

@ -918,17 +918,21 @@ static int proc_sys_compare(const struct dentry *dentry,
struct ctl_table_header *head;
struct inode *inode;
/* Although proc doesn't have negative dentries, rcu-walk means
* that inode here can be NULL */
/* AV: can it, indeed? */
inode = d_inode_rcu(dentry);
if (!inode)
return 1;
if (name->len != len)
return 1;
if (memcmp(name->name, str, len))
return 1;
head = rcu_dereference(PROC_I(inode)->sysctl);
// false positive is fine here - we'll recheck anyway
if (d_in_lookup(dentry))
return 0;
inode = d_inode_rcu(dentry);
// we just might have run into dentry in the middle of __dentry_kill()
if (!inode)
return 1;
head = READ_ONCE(PROC_I(inode)->sysctl);
return !head || !sysctl_is_seen(head);
}