Add NULL check in ns_lookup_list_search for DNS resolution#4844
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sumleo wants to merge 1 commit intobytecodealliance:mainfrom
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Add NULL check in ns_lookup_list_search for DNS resolution#4844sumleo wants to merge 1 commit intobytecodealliance:mainfrom
sumleo wants to merge 1 commit intobytecodealliance:mainfrom
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When no DNS allowlist is configured via --allow-resolve, wasi_ctx->ns_lookup_list is NULL. This NULL pointer gets passed to ns_lookup_list_search which dereferences it unconditionally at the while (*list) loop, causing a crash. A guest WASM module can trigger this by calling sock_addr_resolve.
sumleo
requested review from
TianlongLiang,
lum1n0us,
no1wudi and
yamt
as code owners
lum1n0us
reviewed
Mar 3, 2026
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| size_t host_len = strlen(host), suffix_len; | ||
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| if (!list) |
Contributor
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This is a good practice on defensive programing skills.
But WAMR tends to use a caller-guarantee policy. Caller should make sure their inputs are correct. In this case, wash-app should check inputs before uses Wasm/WASI APIs.
Therefore, I tend to reject this PR.
Contributor
Author
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Closing this PR. After considering the feedback, I agree with the caller-guarantee policy — WAMR expects callers to ensure correct inputs before using WASI APIs, so adding defensive null-checks in the sandboxed system primitives layer is not aligned with the project design philosophy. Thanks for the review. |
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Summary
Fix a NULL pointer dereference in
ns_lookup_list_search()that causes a crash when no DNS allowlist is configured.Problem
When the WASI runtime is started without
--allow-resolve,wasi_ctx->ns_lookup_listis NULL. When a guest WASM module callssock_addr_resolve, the call chain eventually reachesns_lookup_list_search()inposix.c, which dereferences thelistparameter unconditionally atwhile (*list)(line 77). This causes a segmentation fault.Fix
Add a NULL check for the
listparameter before thewhile (*list)loop. Iflistis NULL (no DNS allowlist configured), the function returnsfalse, correctly denying the DNS lookup without crashing.Test
Verified that without
--allow-resolve, callingsock_addr_resolvefrom a WASM module no longer crashes the runtime and instead returns an appropriate error.