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net_nfs3: stop bitmap walks after truncated replies - #19974
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NFSv4 bitmap word counts come from the server. Once an XDR cursor failed, two loops kept decrementing the declared count, allowing a short reply to consume billions of iterations. Stop both walks on cursor failure, matching the existing reclaim path.
Fixed-size fields in replies (stateids, verifiers, the session id) are read through xdr_get_fixed and xdr_skip, so the cursor never passes the end of a reply; nfs4_res reports a cut-short result as NFS4ERR_BADXDR rather than NFS4_OK. OPEN results share one parser for create and reclaim and READDIR pages one taker for v3 and v4, each leaving the caller's state alone for a truncated reply, and xdr_get_opaque checks a length and its pad apart so neither wraps on 32-bit targets. samples/network/nfs_retro/nfs_reply_bounds_test drives these decoders on short and hostile replies placed at the end of their allocations; local_unfs3_test.sh runs it ahead of the server matrix.
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NFSv4 bitmap word counts in fattr4 and OPEN replies come from the
server. nfs4_get_fattr() and nfs4_open_create() keep decrementing the
declared count after the XDR cursor has failed, so a short malicious
reply with a maximum count forces billions of iterations and stalls the
frontend.
Stop the bitmap walks when the cursor fails, matching the existing safe
nfs4_open_reclaim() path. This preserves support for extra bitmap words
while bounding the work to bytes actually received.