linux-ext4 - [Bug 199185] Invalid pointer dereference in get_acl (fs/posix_acl.c) when mounting and operating crafted ext4 image

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Message-ID: <bug-199185-13602-ZuG4g0rcgU@https.bugzilla.kernel.org/>
Date:   Tue, 27 Mar 2018 02:28:49 +0000
From:   bugzilla-daemon@...zilla.kernel.org
To:     linux-ext4@...nel.org
Subject: [Bug 199185] Invalid pointer dereference in get_acl (fs/posix_acl.c)
 when mounting and operating crafted ext4 image

https://bugzilla.kernel.org/show_bug.cgi?id=199185

Eric Biggers (ebiggers3@...il.com) changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ebiggers3@...il.com

--- Comment #4 from Eric Biggers (ebiggers3@...il.com) ---
The above patch is wrong; it makes ext4_get_acl() always fail with ERANGE,
because ext4_get_acl() uses buffer=NULL and buffer_size=0 to get the size of
the xattr.  Likewise getxattr(..., NULL, 0) is broken.  I think we should check
'size' against XATTR_SIZE_MAX in the !buffer case instead.  Also checking 'size
< 0' is unnecessary since 'size' is unsigned.

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