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authorAmir Goldstein <amir73il@gmail.com>2022-08-16 17:53:17 +0300
committerAl Viro <viro@zeniv.linux.org.uk>2022-08-16 17:59:54 +0300
commitd6da19c9cace63290ccfccb1fc35151ffefc0bec (patch)
tree00e66911e1e16675007d324b91572ab73adac346 /fs/open.c
parent568035b01cfb107af8d2e4bd2fb9aea22cf5b868 (diff)
downloadlinux-d6da19c9cace63290ccfccb1fc35151ffefc0bec.tar.xz
locks: fix TOCTOU race when granting write lease
Thread A trying to acquire a write lease checks the value of i_readcount and i_writecount in check_conflicting_open() to verify that its own fd is the only fd referencing the file. Thread B trying to open the file for read will call break_lease() in do_dentry_open() before incrementing i_readcount, which leaves a small window where thread A can acquire the write lease and then thread B completes the open of the file for read without breaking the write lease that was acquired by thread A. Fix this race by incrementing i_readcount before checking for existing leases, same as the case with i_writecount. Use a helper put_file_access() to decrement i_readcount or i_writecount in do_dentry_open() and __fput(). Fixes: 387e3746d01c ("locks: eliminate false positive conflicts for write lease") Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/open.c')
-rw-r--r--fs/open.c11
1 files changed, 4 insertions, 7 deletions
diff --git a/fs/open.c b/fs/open.c
index 8a813fa5ca56..a98572585815 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -840,7 +840,9 @@ static int do_dentry_open(struct file *f,
return 0;
}
- if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) {
+ if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) {
+ i_readcount_inc(inode);
+ } else if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) {
error = get_write_access(inode);
if (unlikely(error))
goto cleanup_file;
@@ -880,8 +882,6 @@ static int do_dentry_open(struct file *f,
goto cleanup_all;
}
f->f_mode |= FMODE_OPENED;
- if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
- i_readcount_inc(inode);
if ((f->f_mode & FMODE_READ) &&
likely(f->f_op->read || f->f_op->read_iter))
f->f_mode |= FMODE_CAN_READ;
@@ -935,10 +935,7 @@ cleanup_all:
if (WARN_ON_ONCE(error > 0))
error = -EINVAL;
fops_put(f->f_op);
- if (f->f_mode & FMODE_WRITER) {
- put_write_access(inode);
- __mnt_drop_write(f->f_path.mnt);
- }
+ put_file_access(f);
cleanup_file:
path_put(&f->f_path);
f->f_path.mnt = NULL;