Fix dentry hash collisions that prevented boot with selinux enabled (rhbz 805371)

1 files changed, 113 insertions, 0 deletions

diff --git a/fix-dentry-hash.patch b/fix-dentry-hash.patch
new file mode 100644
index 00000000..c5b2f477
--- /dev/null
+++ b/fix-dentry-hash.patch
@@ -0,0 +1,113 @@
+From davej  Thu Mar 22 16:38:38 2012
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+Date:	Thu, 22 Mar 2012 20:36:58 +0000
+From: Al Viro <viro@ZenIV.linux.org.uk>
+To: Linus Torvalds <torvalds@linux-foundation.org>
+Cc: linux-kernel@vger.kernel.org, xen-devel@lists.xensource.com,
+        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
+Subject: Re: Regression introduced by
+ bfcfaa77bdf0f775263e906015982a608df01c76 (vfs: use 'unsigned long' accesses
+ for dcache name comparison and hashing)
+Message-ID: <20120322203658.GC6589@ZenIV.linux.org.uk>
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+
+On Thu, Mar 22, 2012 at 08:24:45PM +0000, Al Viro wrote:
+> 
+> OK, full_name_hash()/hash_name() definitely have a mismatch and it's on the
+> names of length 8*n: trivial experiment shows that we have
+> name hash_name full_name_hash
+> a 61 61
+> ab 6261 6261
+> abc 636261 636261
+> abcd 64636261 64636261
+> abcdabc 64c6c4c2 64c6c4c2
+> abcdabcd efcead5 c8c6c4c2
+> abcdabcd9 efceb0e efceb0e
+> 
+> Linus, which way do you prefer to shift it?  Should hash_name() change to
+> match full_name_hash() or should it be the other way round?
+> 
+> What happens is that you get multiplication by 9 and adding 0 in the former,
+> after having added the last full word.  In the latter we add the last full
+> word, see that there's nothing left and bugger off.
+
+Guys, could you check if this fixes it?
+
+diff --git a/fs/namei.c b/fs/namei.c
+index 13e6a1f..7451d6f8 100644
+--- a/fs/namei.c
++++ b/fs/namei.c
+@@ -1439,10 +1439,10 @@ unsigned int full_name_hash(const unsigned char *name, unsigned int len)
+ 
+ 	for (;;) {
+ 		a = *(unsigned long *)name;
+-		hash *= 9;
+ 		if (len < sizeof(unsigned long))
+ 			break;
+ 		hash += a;
++		hash *= 9;
+ 		name += sizeof(unsigned long);
+ 		len -= sizeof(unsigned long);
+ 		if (!len)
+--
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