5.4-stable review patch. If anyone has any objections, please let me know.
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From: Kees Cook kees@kernel.org
[ 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 --- fs/overlayfs/util.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c index 4d75e1cdf0b9c..af813e7773795 100644 --- a/fs/overlayfs/util.c +++ b/fs/overlayfs/util.c @@ -191,7 +191,9 @@ enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path)
struct dentry *ovl_dentry_upper(struct dentry *dentry) { - return ovl_upperdentry_dereference(OVL_I(d_inode(dentry))); + struct inode *inode = d_inode(dentry); + + return inode ? ovl_upperdentry_dereference(OVL_I(inode)) : NULL; }
struct dentry *ovl_dentry_lower(struct dentry *dentry)