[PATCH v5 1/2] vfs: allow dedupe of user owned read-only files
The permission check in vfs_dedupe_file_range() is too coarse - We
only allow dedupe of the destination file if the user is root, or
they have the file open for write.
This effectively limits a non-root user from deduping their own read-only
files. In addition, the write file descriptor that the user is forced to
hold open can prevent execution of files. As file data during a dedupe
does not change, the behavior is unexpected and this has caused a number of
issue reports. For an example, see:
https://github.com/markfasheh/duperemove/issues/129
So change the check so we allow dedupe on the target if:
- the root or admin is asking for it
- the process has write access
- the owner of the file is asking for the dedupe
- the process could get write access
That way users can open read-only and still get dedupe.
Signed-off-by: Mark Fasheh
Acked-by: Darrick J. Wong
---
fs/read_write.c | 17 +++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/fs/read_write.c b/fs/read_write.c
index e83bd9744b5d..71e9077f8bc1 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1964,6 +1964,20 @@ int vfs_dedupe_file_range_compare(struct inode *src,
loff_t srcoff,
}
EXPORT_SYMBOL(vfs_dedupe_file_range_compare);
+/* Check whether we are allowed to dedupe the destination file */
+static bool allow_file_dedupe(struct file *file)
+{
+ if (capable(CAP_SYS_ADMIN))
+ return true;
+ if (file->f_mode & FMODE_WRITE)
+ return true;
+ if (uid_eq(current_fsuid(), file_inode(file)->i_uid))
+ return true;
+ if (!inode_permission(file_inode(file), MAY_WRITE))
+ return true;
+ return false;
+}
+
int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same)
{
struct file_dedupe_range_info *info;
@@ -1972,7 +1986,6 @@ int vfs_dedupe_file_range(struct file *file, struct
file_dedupe_range *same)
u64 len;
int i;
int ret;
- bool is_admin = capable(CAP_SYS_ADMIN);
u16 count = same->dest_count;
struct file *dst_file;
loff_t dst_off;
@@ -2036,7 +2049,7 @@ int vfs_dedupe_file_range(struct file *file, struct
file_dedupe_range *same)
if (info->reserved) {
info->status = -EINVAL;
- } else if (!(is_admin || (dst_file->f_mode & FMODE_WRITE))) {
+ } else if (!allow_file_dedupe(dst_file)) {
info->status = -EINVAL;
} else if (file->f_path.mnt != dst_file->f_path.mnt) {
info->status = -EXDEV;
--
2.15.1
[PATCH v5 1/2] vfs: allow dedupe of user owned read-only files
The permission check in vfs_dedupe_file_range() is too coarse - We
only allow dedupe of the destination file if the user is root, or
they have the file open for write.
This effectively limits a non-root user from deduping their own read-only
files. In addition, the write file descriptor that the user is forced to
hold open can prevent execution of files. As file data during a dedupe
does not change, the behavior is unexpected and this has caused a number of
issue reports. For an example, see:
https://github.com/markfasheh/duperemove/issues/129
So change the check so we allow dedupe on the target if:
- the root or admin is asking for it
- the process has write access
- the owner of the file is asking for the dedupe
- the process could get write access
That way users can open read-only and still get dedupe.
Signed-off-by: Mark Fasheh
Acked-by: Darrick J. Wong
---
fs/read_write.c | 17 +++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/fs/read_write.c b/fs/read_write.c
index e83bd9744b5d..71e9077f8bc1 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1964,6 +1964,20 @@ int vfs_dedupe_file_range_compare(struct inode *src,
loff_t srcoff,
}
EXPORT_SYMBOL(vfs_dedupe_file_range_compare);
+/* Check whether we are allowed to dedupe the destination file */
+static bool allow_file_dedupe(struct file *file)
+{
+ if (capable(CAP_SYS_ADMIN))
+ return true;
+ if (file->f_mode & FMODE_WRITE)
+ return true;
+ if (uid_eq(current_fsuid(), file_inode(file)->i_uid))
+ return true;
+ if (!inode_permission(file_inode(file), MAY_WRITE))
+ return true;
+ return false;
+}
+
int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same)
{
struct file_dedupe_range_info *info;
@@ -1972,7 +1986,6 @@ int vfs_dedupe_file_range(struct file *file, struct
file_dedupe_range *same)
u64 len;
int i;
int ret;
- bool is_admin = capable(CAP_SYS_ADMIN);
u16 count = same->dest_count;
struct file *dst_file;
loff_t dst_off;
@@ -2036,7 +2049,7 @@ int vfs_dedupe_file_range(struct file *file, struct
file_dedupe_range *same)
if (info->reserved) {
info->status = -EINVAL;
- } else if (!(is_admin || (dst_file->f_mode & FMODE_WRITE))) {
+ } else if (!allow_file_dedupe(dst_file)) {
info->status = -EINVAL;
} else if (file->f_path.mnt != dst_file->f_path.mnt) {
info->status = -EXDEV;
--
2.15.1
--
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