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authorGustavo A. R. Silva <gustavo@embeddedor.com>2020-03-09 15:22:33 -0500
committerMiklos Szeredi <mszeredi@redhat.com>2020-03-17 15:04:23 +0100
commit0efbe7c4f948eb1233ef52c1cdba0b4ff973df36 (patch)
treeee4c0c236d1e706f8bbe8d2c18a83e48b4c1414d /fs/overlayfs
parent504f38410a51f513606c3c18c7f6a32c1ca2afb5 (diff)
ovl: replace zero-length array with flexible-array member
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com> Fixes: cbe7fba8edfc ("ovl: make sure that real fid is 32bit aligned in memory") Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Diffstat (limited to 'fs/overlayfs')
-rw-r--r--fs/overlayfs/overlayfs.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index ea531b1075f2..e81fea86139e 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -87,7 +87,7 @@ struct ovl_fb {
u8 flags; /* OVL_FH_FLAG_* */
u8 type; /* fid_type of fid */
uuid_t uuid; /* uuid of filesystem */
- u32 fid[0]; /* file identifier should be 32bit aligned in-memory */
+ u32 fid[]; /* file identifier should be 32bit aligned in-memory */
} __packed;
/* In-memory and on-wire format for overlay file handle */