Hi,
Thanks for the report and the testcase.
Here's a patch using a different approach (overlayfs philosophy is to minimize
VFS footprint).
Thanks,
Miklos
---
From: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Subject: ovl: get_write_access() in truncate
When truncating a file we should check write access on the underlying
inode. And we should do so on the lower file as well (before copy-up) for
consistency.
Original patch and test case by Aihua Zhang.
- - >o >o - - test.c - - >o >o - -
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
int ret;
ret = truncate(argv[0], 4096);
if (ret != -1) {
fprintf(stderr, "truncate(argv[0]) should have failed\n");
return 1;
}
if (errno != ETXTBSY) {
perror("truncate(argv[0])");
return 1;
}
return 0;
}
- - >o >o - - >o >o - - >o >o - -
Reported-by: Aihua Zhang <zhangaihua1@xxxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
fs/overlayfs/inode.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -59,16 +59,37 @@ int ovl_setattr(struct dentry *dentry, s
if (err)
goto out;
+ if (attr->ia_valid & ATTR_SIZE) {
+ struct inode *realinode = d_inode(ovl_dentry_real(dentry));
+
+ err = -ETXTBSY;
+ if (atomic_read(&realinode->i_writecount) < 0)
+ goto out_drop_write;
+ }
+
err = ovl_copy_up(dentry);
if (!err) {
+ struct inode *winode = NULL;
+
upperdentry = ovl_dentry_upper(dentry);
+ if (attr->ia_valid & ATTR_SIZE) {
+ winode = d_inode(upperdentry);
+ err = get_write_access(winode);
+ if (err)
+ goto out_drop_write;
+ }
+
inode_lock(upperdentry->d_inode);
err = notify_change(upperdentry, attr, NULL);
if (!err)
ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
inode_unlock(upperdentry->d_inode);
+
+ if (winode)
+ put_write_access(winode);
}
+out_drop_write:
ovl_drop_write(dentry);
out:
return err;
--
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