From: Aleksa Sarai Date: Tue, 31 Mar 2026 14:46:21 +0000 (+1100) Subject: dcache: permit dynamic_dname()s up to NAME_MAX X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=97b67e64affb0e709eeecc50f6a9222fc20bd14b;p=thirdparty%2Fkernel%2Flinux.git dcache: permit dynamic_dname()s up to NAME_MAX dynamic_dname() has had an implicit limit of 64 characters since it was introduced in commit c23fbb6bcb3e ("VFS: delay the dentry name generation on sockets and pipes"), however it seems that this was a fairly arbitrary number (suspiciously it was double the previously hardcoded buffer size). NAME_MAX seems like a more reasonable and consistent limit for d_name lengths. While we're at it, we can also remove the unnecessary stack-allocated array and just memmove() the formatted string to the end of the buffer. It should also be noted that at least one driver (in particular, liveupdate's usage of anon_inode for session files) already exceeded this limit without noticing that readlink(/proc/self/fd/$n) always returns -ENAMETOOLONG, so this fixes those drivers as well. Fixes: 0153094d03df ("liveupdate: luo_session: add sessions support") Fixes: c23fbb6bcb3e ("VFS: delay the dentry name generation on sockets and pipes") Signed-off-by: Aleksa Sarai Link: https://patch.msgid.link/20260401-dynamic-dname-name_max-v1-1-8ca20ab2642e@amutable.com Tested-by: Luca Boccassi Signed-off-by: Christian Brauner --- diff --git a/fs/d_path.c b/fs/d_path.c index bb365511066b2..a48957c0971ef 100644 --- a/fs/d_path.c +++ b/fs/d_path.c @@ -301,18 +301,19 @@ EXPORT_SYMBOL(d_path); char *dynamic_dname(char *buffer, int buflen, const char *fmt, ...) { va_list args; - char temp[64]; + char *start; int sz; va_start(args, fmt); - sz = vsnprintf(temp, sizeof(temp), fmt, args) + 1; + sz = vsnprintf(buffer, buflen, fmt, args) + 1; va_end(args); - if (sz > sizeof(temp) || sz > buflen) + if (sz > NAME_MAX || sz > buflen) return ERR_PTR(-ENAMETOOLONG); - buffer += buflen - sz; - return memcpy(buffer, temp, sz); + /* Move the formatted d_name to the end of the buffer. */ + start = buffer + (buflen - sz); + return memmove(start, buffer, sz); } char *simple_dname(struct dentry *dentry, char *buffer, int buflen)