querier: fix active query tracker panic on UTF-8 continuation bytes (fixes #7729) - #7771
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trimStringByBytes scans backwards from the truncation point to find a
UTF-8 rune start, but the loop had no lower bound. When a request field
consists only of UTF-8 continuation bytes (0x80-0xBF) there is no rune
start to land on, so size underflows past zero and bytesStr[-1] panics
with 'index out of range [-1]'. Because the active query tracker is
enabled by default and the panic happens on a goroutine without recover(),
an attacker-supplied match[]/query value can crash the querier.
Bound the scan with 'size > 0' so it stops at the start of the string
instead of underflowing. When no rune start exists the field is truncated
to an empty string, which is safe.
Add TestTrimForJsonMarshalContinuationBytes covering the all-continuation-
byte case; existing multi-byte tests use valid UTF-8 ('世') which always
terminates the scan at index 0 and therefore never exercised the underflow.
Fixes cortexproject#7729
Signed-off-by: ...
Signed-off-by: Mehrdad Biukian Naeini <mehrdad.biu@mtnirancell.ir>
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Summary
Fixes #7729.
trimStringByBytes(pkg/util/request_tracker/request_extractor.go) scans backwards from the truncation point to find a UTF-8 rune start, but the loop had no lower bound. When a request field consists only of UTF-8 continuation bytes (0x80–0xBF) there is no rune start to land on, sosizeunderflows past zero andbytesStr[-1]panics withindex out of range [-1]. Since the active query tracker is enabled by default and the panic occurs on a goroutine withoutrecover(), an attacker-suppliedmatch[]/queryvalue can crash the querier (crash-loop on repeat).The fix bounds the scan with
size > 0. When no rune start exists, the field is truncated to an empty string, which is safe and still produces valid JSON.Verification
TestTrimForJsonMarshalContinuationByteswith 1200 continuation bytes (\x80) truncated to size 900.runtime error: index out of range [-1].pkg/util/request_trackersuite passes.gofmt -lclean on changed files.This is the same class of panic #7640 addressed in
trimForJsonMarshalRecursive; that PR added arepeatSize <= 0guard but did not touch the underflow insidetrimStringByBytes, and its regression tests used only valid multi-byte UTF-8 (世) which always terminates the backwards scan at index 0.Signed-off-by: ...