fix(epbf): fix behavior of has_prefix() and add strncmp()
#4394
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oshaked1
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yanivagman
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Nov 25, 2024
pkg/ebpf/c/tracee.bpf.c
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| @@ -3140,7 +3140,7 @@ statfunc int capture_file_write(struct pt_regs *ctx, u32 event_id, bool is_buf) | |||
| // otherwise the capture will overwrite itself. | |||
| int pid = 0; | |||
| void *path_buf = get_path_str_cached(file); | |||
| if (path_buf != NULL && has_prefix("/dev/null", (char *) path_buf, 10)) { | |||
| if (path_buf != NULL && strncmp("/dev/null", (char *) path_buf, 9) == 0) { | |||
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In this case, don't we want to compare 10 bytes to take into account null byte as well?
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You're right I'll change it
There are 2 implementations for `has_prefix()`, one as a macro and one as a function (depending on the compiler version). They both behave differently in cases where no difference was found in `n` iterations - the macro returns 1 (true), which is an issue if the prefix is longer than `n`, while the function returns 0 (false) which is wrong if the prefix and string are identical. An additional check was added to `has_prefix()` to account for prefixes longer than `n`, while still returning true when the strings are equal. Additionally, an `strncmp()` macro and function were added, because most uses of `has_prefix()` become clearer when using `strncmp()`. Only a single usage of `has_prefix()` (in `filter_file_path()`) cannot use `strncmp()` because the prefix length can only be determined at runtime which makes usage of an unrolled loop impossible. Instead, it must use `has_prefix()` which accounts for prefixes shorter than the string, unlike `strncmp()`.
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Closes #4395
There are 2 implementations for
has_prefix(), one as a macro and one as a function (depending on the compiler version). They both behave differently in cases where no difference was found inniterations - the macro returns 1 (true), which is an issue if the prefix is longer thann, while the function returns 0 (false) which is wrong if the prefix and string are identical. An additional check was added tohas_prefix()to account for prefixes longer thann, while still returning true when the strings are equal.Additionally, an
strncmp()macro and function were added, because most uses ofhas_prefix()become clearer when usingstrncmp().Only a single usage of
has_prefix()(infilter_file_path()) cannot usestrncmp()because the prefix length can only be determined at runtime which makes usage of an unrolled loop impossible. Instead, it must usehas_prefix()which accounts for prefixes shorter than the string, unlikestrncmp().