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input_thread: replace raw read() with pipe abstraction to fix crash #11623

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Merged
edsiper merged 1 commit into from
Apr 14, 2026
Merged

input_thread: replace raw read() with pipe abstraction to fix crash #11623

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4 changes: 2 additions & 2 deletions src/flb_input_thread.c
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Original file line number Diff line number Diff line change
Expand Up @@ -59,9 +59,9 @@ static inline int handle_input_event(flb_pipefd_t fd, struct flb_input_instance
uint64_t val;
struct flb_config *config = ins->config;

bytes = read(fd, &val, sizeof(val));
bytes = flb_pipe_r(fd, &val, sizeof(val));
if (bytes == -1) {
flb_errno();
flb_pipe_error();
return -1;
Comment on lines +62 to 65

@coderabbitai coderabbitai Bot Mar 27, 2026

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⚠️ Potential issue | 🟠 Major

🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
set -euo pipefail

echo "== Locate mk_event_channel_create implementation/usages =="
rg -n -C3 'mk_event_channel_create|socketpair|pipe\(|recv\(|send\('

echo
echo "== Locate fixed-size flb_pipe_r reads and their guards =="
rg -n -C4 'flb_pipe_r\([^;]*sizeof\((val|uint64_t)\)\)' src include

echo
echo "== Inspect guards around handle_input_event and handle_input_thread_event =="
rg -n -C6 'handle_input_event|handle_input_thread_event|bytes == -1|bytes <= 0|bytes != sizeof' src/flb_input_thread.c

Repository: fluent/fluent-bit

Length of output: 50374

🏁 Script executed:

#!/bin/bash
set -euo pipefail

echo "=== Reading src/flb_input_thread.c lines 50-80 ==="
sed -n '50,80p' src/flb_input_thread.c

echo ""
echo "=== Checking flb_pipe.h for flb_pipe_r definition ==="
rg -n "^[^/]*flb_pipe_r" include/fluent-bit/flb_pipe.h -A 5

echo ""
echo "=== Looking for all guard patterns after flb_pipe_r calls ==="
rg -n -A 2 'flb_pipe_r.*sizeof' src/flb_input_thread.c

echo ""
echo "=== Checking both handler functions in detail ==="
rg -n -B 5 -A 8 'handle_input_event|handle_input_thread_event' src/flb_input_thread.c | head -80

Repository: fluent/fluent-bit

Length of output: 3962

🏁 Script executed:

#!/bin/bash
set -euo pipefail

echo "=== Search for all fixed-size flb_pipe_r reads ==="
rg -n 'flb_pipe_r.*sizeof.*uint64_t|flb_pipe_r.*sizeof.*output_flush' src/ -A 3 | head -60

echo ""
echo "=== Check if short-read validation exists anywhere for fixed-size protocol messages ==="
rg -n 'bytes != sizeof|ret != sizeof' src/flb_input_thread.c src/flb_output_thread.c

echo ""
echo "=== Verify the exact bit-field macros being used ==="
rg -n 'FLB_BITS_U64_HIGH|FLB_BITS_U64_LOW' include/fluent-bit/ -B 1 -A 1 | head -30

Repository: fluent/fluent-bit

Length of output: 1303

🏁 Script executed:

#!/bin/bash
set -euo pusedo pipefail

echo "=== Check mk_event_channel_create to understand channel semantics ==="
rg -n 'mk_event_channel_create' lib/monkey/include/monkey/ -A 15 2>/dev/null | head -50

echo ""
echo "=== Search for short-read handling in flb_pipe_write_all and flb_pipe_read_all ==="
cat src/flb_pipe.c 2>/dev/null || echo "File may not exist or other error"

Repository: fluent/fluent-bit

Length of output: 112

🏁 Script executed:

#!/bin/bash
set -euo pipefail

echo "=== Search for flb_pipe_read_all and flb_pipe_write_all implementations ==="
cat src/flb_pipe.c

echo ""
echo "=== Check if there's any documentation on atomicity ==="
rg -n 'socketpair|mk_event_channel' include/fluent-bit/ -B 2 -A 5 | head -60

Repository: fluent/fluent-bit

Length of output: 5485

Check guards before decoding fixed-size protocol messages in event handlers.

Lines 63 and 107 only reject -1. With flb_pipe_r() (wrapping recv/read), returning 0 (closed peer) or short positive reads is possible. Without validating full message reception, partial val data will corrupt bit-field extraction and misroute events.

Proposed fix 
     bytes = flb_pipe_r(fd, &val, sizeof(val));
-    if (bytes == -1) {
+    if (bytes <= 0) {
         flb_pipe_error();
         return -1;
     }
+    if (bytes != sizeof(val)) {
+        flb_error("[thread event loop] short read on fd=%i, got=%i expected=%zu",
+                  fd, bytes, sizeof(val));
+        return -1;
+    }

Similar patterns exist at lines 437–438 and 774–775 in the same file, though they use only <= 0 checks without validating message completeness. Both handle_input_event and handle_input_thread_event need this fix.

🤖 Prompt for AI Agents 
Verify each finding against the current code and only fix it if needed.

In `@src/flb_input_thread.c` around lines 62 - 65, The handlers currently call
flb_pipe_r(fd, &val, sizeof(val)) and only treat bytes == -1 (or <= 0) as
errors, which allows 0 (peer closed) or short reads to proceed and corrupt the
decoded bit-field; in handle_input_event and handle_input_thread_event update
the read handling to verify that the returned bytes == sizeof(val) and treat any
other return (0 or short read or -1) as an error/closed peer path (call
flb_pipe_error() or the existing cleanup flow), and apply the same full-length
validation to the other occurrences of flb_pipe_r reading fixed-size protocol
messages so you never decode a partially-populated val.

}

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