path: root/src
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authorRich Felker <>2022-06-03 11:03:00 -0400
committerRich Felker <>2022-06-03 11:03:00 -0400
commit6c858d6fd4df8b5498ef2cae66c8f3c3eff1587b (patch)
tree0db4e25788d0be57296f645cd51e10b9713a0a94 /src
parent8974ef2124118e4ed8cad7ee0534b36e5c584c4e (diff)
ensure distinct query id for parallel A and AAAA queries in resolver
assuming a reasonable realtime clock, res_mkquery is highly unlikely to generate the same query id twice in a row, but it's possible with a very low-resolution system clock or under extreme delay of forward progress. when it happens, res_msend fails to wait for both answers, and instead stops listening after getting two answers to the same query (A or AAAA). to avoid this, increment one byte of the second query's id if it matches the first query's. don't bother checking if the second byte is also equal, since it doesn't matter; we just need to ensure that at least one byte is distinct.
Diffstat (limited to 'src')
1 files changed, 3 insertions, 0 deletions
diff --git a/src/network/lookup_name.c b/src/network/lookup_name.c
index aa558c19..b5232ce8 100644
--- a/src/network/lookup_name.c
+++ b/src/network/lookup_name.c
@@ -155,6 +155,9 @@ static int name_from_dns(struct address buf[static MAXADDRS], char canon[static
if (qlens[nq] == -1)
return EAI_NONAME;
qbuf[nq][3] = 0; /* don't need AD flag */
+ /* Ensure query IDs are distinct. */
+ if (nq && qbuf[nq][0] == qbuf[0][0])
+ qbuf[nq][0]++;