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[ Upstream commit 8a39f1c870e9d6fbac5638f3a42a6a6363829c49 ]
In ovl_path_type() and ovl_is_metacopy_dentry() GCC notices that it is
possible for OVL_E() to return NULL (which implies that d_inode(dentry)
may be NULL). This would result in out of bounds reads via container_of(),
seen with GCC 15's -Warray-bounds -fdiagnostics-details. For example:
In file included from arch/x86/include/generated/asm/rwonce.h:1,
from include/linux/compiler.h:339,
from include/linux/export.h:5,
from include/linux/linkage.h:7,
from include/linux/fs.h:5,
from fs/overlayfs/util.c:7:
In function 'ovl_upperdentry_dereference',
inlined from 'ovl_dentry_upper' at ../fs/overlayfs/util.c:305:9,
inlined from 'ovl_path_type' at ../fs/overlayfs/util.c:216:6:
include/asm-generic/rwonce.h:44:26: error: array subscript 0 is outside array bounds of 'struct inode[7486503276667837]' [-Werror=array-bounds=]
44 | #define __READ_ONCE(x) (*(const volatile __unqual_scalar_typeof(x) *)&(x))
| ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/asm-generic/rwonce.h:50:9: note: in expansion of macro '__READ_ONCE'
50 | __READ_ONCE(x); \
| ^~~~~~~~~~~
fs/overlayfs/ovl_entry.h:195:16: note: in expansion of macro 'READ_ONCE'
195 | return READ_ONCE(oi->__upperdentry);
| ^~~~~~~~~
'ovl_path_type': event 1
185 | return inode ? OVL_I(inode)->oe : NULL;
'ovl_path_type': event 2
Avoid this by allowing ovl_dentry_upper() to return NULL if d_inode() is
NULL, as that means the problematic dereferencing can never be reached.
Note that this fixes the over-eager compiler warning in an effort to
being able to enable -Warray-bounds globally. There is no known
behavioral bug here.
Suggested-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Kees Cook <kees@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.