path: bound directory-walk recursion depth to prevent stack overflow - #45
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walk_path_recursive() recursed once per directory level with no depth limit. A remote SFTP server (malicious or compromised) can present an arbitrarily deep directory hierarchy, causing the client to recurse until the thread stack is exhausted and the process crashes (SIGSEGV), aborting the transfer. Reproduced locally: a 400-level-deep local directory tree crashes the unpatched walk_src_path() with a segmentation fault (stack overflow). With this patch, the same tree is rejected cleanly with a 'directory nesting too deep' error and no crash. Add a depth counter threaded through walk_path_recursive(), bailing out at 256 levels -- deep enough for any realistic directory layout while keeping stack usage to roughly 1-2MB, well within the default 8MB thread stack.
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walk_path_recursive() recurses once per directory level with no depth limit. A remote SFTP server (malicious or just compromised) can hand back an arbitrarily deep directory tree, and the client will keep recursing until the thread stack runs out and the process crashes.
I reproduced this locally: a 400-level-deep directory tree segfaults the current code. This patch adds a depth counter and bails out with an error past 256 levels, which is far deeper than any real directory layout needs and keeps stack usage to a couple MB.