Hi Joel,
On 2024-08-05 11:39:35+0000, Thomas Weißschuh wrote:
The test if a table is a permanently empty one, inspects the address of the registered ctl_table argument. However as sysctl_mount_point is an empty array and does not occupy and space it can end up sharing an address with another object in memory. If that other object itself is a "struct ctl_table" then registering that table will fail as it's incorrectly recognized as permanently empty.
Avoid this issue by adding a dummy element to the array so that is not empty anymore. Explicitly register the table with zero elements as otherwise the dummy element would be recognized as a sentinel element which would lead to a runtime warning from the sysctl core.
While the issue seems not being encountered at this time, this seems mostly to be due to luck. Also a future change, constifying sysctl_mount_point and root_table, can reliably trigger this issue on clang 18.
Given that empty arrays are non-standard in the first place it seems prudent to avoid them if possible.
Fixes: 4a7b29f65094 ("sysctl: move sysctl type to ctl_table_header") Fixes: a35dd3a786f5 ("sysctl: drop now unnecessary out-of-bounds check") Cc: stable@vger.kernel.org Signed-off-by: Thomas Weißschuh linux@weissschuh.net
Any updates on this? I fear it can theoretically also happen on v6.11.
fs/proc/proc_sysctl.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c index 9553e77c9d31..d11ebc055ce0 100644 --- a/fs/proc/proc_sysctl.c +++ b/fs/proc/proc_sysctl.c @@ -29,8 +29,13 @@ static const struct inode_operations proc_sys_inode_operations; static const struct file_operations proc_sys_dir_file_operations; static const struct inode_operations proc_sys_dir_operations; -/* Support for permanently empty directories */ -static struct ctl_table sysctl_mount_point[] = { }; +/*
- Support for permanently empty directories.
- Must be non-empty to avoid sharing an address with other tables.
- */
+static struct ctl_table sysctl_mount_point[] = {
- { }
+}; /**
- register_sysctl_mount_point() - registers a sysctl mount point
@@ -42,7 +47,7 @@ static struct ctl_table sysctl_mount_point[] = { }; */ struct ctl_table_header *register_sysctl_mount_point(const char *path) {
- return register_sysctl(path, sysctl_mount_point);
- return register_sysctl_sz(path, sysctl_mount_point, 0);
} EXPORT_SYMBOL(register_sysctl_mount_point);
-- 2.46.0