7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kazuki Hanai [ Upstream commit f439d79e8cd19f89e04cbb3b532347edacd72c79 ] shmem_parse_opt_casefold() stores the unicode_map returned by utf8_load() in ctx->encoding. A filesystem context can receive the casefold parameter more than once, and a second successful parse overwrites the stored map without releasing it. The map is also leaked when an unmounted filesystem context is freed. This includes the temporary context used for remount, because shmem_reconfigure() does not take ownership of ctx->encoding. Reject a second casefold setting, clear ctx->encoding after transferring ownership to the superblock, and release any remaining map from shmem_free_fc(). An unprivileged user can repeatedly create tmpfs filesystem contexts, set the casefold parameter, and close them from a user namespace. This causes unbounded kernel memory consumption and can result in a local denial of service. Link: https://lore.kernel.org/20261002081306.637148-1-hnkz.64@gmail.com Fixes: 58e55efd6c72 ("tmpfs: Add casefold lookup support") Signed-off-by: Kazuki Hanai Signed-off-by: Andrew Morton Suggested-by: Gabriel Krisman Bertazi Cc: Hugh Dickins Cc: Baolin Wang Cc: André Almeida Cc: Christian Brauner Cc: Signed-off-by: Sasha Levin --- mm/shmem.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/mm/shmem.c b/mm/shmem.c index 93714b47f414b..de2362209cc38 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -4511,6 +4511,9 @@ static int shmem_parse_opt_casefold(struct fs_context *fc, struct fs_parameter * struct unicode_map *encoding; char *version_str = param->string + 5; + if (ctx->encoding) + return invalfc(fc, "casefold parameter cannot be specified twice\n"); + if (!latest_version) { if (strncmp(param->string, "utf8-", 5)) return invalfc(fc, "Only UTF-8 encodings are supported " @@ -5000,6 +5003,7 @@ static int shmem_fill_super(struct super_block *sb, struct fs_context *fc) if (ctx->encoding) { sb->s_encoding = ctx->encoding; + ctx->encoding = NULL; set_default_d_op(sb, &shmem_ci_dentry_ops); if (ctx->strict_encoding) sb->s_encoding_flags = SB_ENC_STRICT_MODE_FL; @@ -5097,6 +5101,9 @@ static void shmem_free_fc(struct fs_context *fc) struct shmem_options *ctx = fc->fs_private; if (ctx) { +#if IS_ENABLED(CONFIG_UNICODE) + utf8_unload(ctx->encoding); +#endif mpol_put(ctx->mpol); kfree(ctx); } -- 2.53.0