cifs: fix memory leak in smb3_fs_context_parse_param error path

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: cifs: fix memory leak in smb3_fs_context_parse_param error path Add proper cleanup of ctx->source and fc->source to the cifs_parse_mount_err error handler. This ensures that memory allocated for the source strings is correctly freed on all error paths, matching the cleanup already performed in the success path by smb3_cleanup_fs_context_contents(). Pointers are also set to NULL after freeing to prevent potential double-free issues. This change fixes a memory leak originally detected by syzbot. The leak occurred when processing Opt_source mount options if an error happened after ctx->source and fc->source were successfully allocated but before the function completed. The specific leak sequence was: 1. ctx->source = smb3_fs_context_fullpath(ctx, '/') allocates memory 2. fc->source = kstrdup(ctx->source, GFP_KERNEL) allocates more memory 3. A subsequent error jumps to cifs_parse_mount_err 4. The old error handler freed passwords but not the source strings, causing the memory to leak. This issue was not addressed by commit e8c73eb7db0a ("cifs: client: fix memory leak in smb3_fs_context_parse_param"), which only fixed leaks from repeated fsconfig() calls but not this error path. Patch updated with minor change suggested by kernel test robot

References

• https://git.kernel.org/stable/c/7627864dc3121f39e220f5253a227edf472de59e
• https://git.kernel.org/stable/c/48d69290270891f988e72edddd9688c20515421d
• https://git.kernel.org/stable/c/37010021d7e0341bb241ca00bcbae31f2c50b23f
• https://git.kernel.org/stable/c/7e4d9120cfa413dd34f4f434befc5dbe6c38b2e5